perpendicular
[p_ˌɜː_p_ə_n_d_ˈɪ_k_j_ʊ_l_ə], [pˌɜːpəndˈɪkjʊlə], [pˌɜːpəndˈɪkjʊlə]Antonyms for perpendicular:
catercorner, diagonal, nonparallel, Monoclinal, catacornered, horizontal, leaning, level, aslope, kittycorner, swimming, cattycornered, sloped, aslant, Obliqueangled, parallel, sideways, recumbent, sagging, gradual, tilted, nonintersecting, canted, supine, slanted, skewed, highpitched, sloping, graded, hanging, catercornered, inclined, slantwise, pitched, salient, listing, lowpitched, flat, catacorner, Raked, tipped, nonconvergent, skew, Tilting, collateral, cant, atilt, crabwise, prostrate, kittycornered, naiant, crosswise, oblique, cattycorner, bias, slanting, sidelong, antiparallel.
Definitions of perpendicular:

extremely steep; " the great perpendicular face of the cliff"
– Wordnet Dictionary DB 
Exactly upright; meeting at right angles.
– The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. 
intersecting at or forming right angles; " the axes are perpendicular to each other"
– Wordnet Dictionary DB 
an extremely steep face
– Wordnet Dictionary DB 
A perpendicular line. See Perpend.
– Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. 
An upright line; a line at right angles with another.
– The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. 
A perpendicular line or plane.
– The american dictionary of the english language. By Daniel Lyons. Published 1899. 
Extending in a straight line to the centre of the earth, or at right angles to the horizon; at right angles to a given line or surface.
– Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. 
Exactly upright or vertical; pointing to the zenith; at right angles to the plane of the horizon; extending in a right line from any point toward the center of the earth.
– Newage Dictionary DB 
Exactly upright: extending in a straight line toward the centre of the earth: ( geom.) at right angles to a given line or surface.
– The american dictionary of the english language. By Daniel Lyons. Published 1899. 
At right angles to a line or surface; upright.
– The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. 
Upright; vertical; meeting a given line at right angles.
– The Concise Standard Dictionary of the English Language. By James Champlin Fernald. Published 1919. 
Perpendicularly.
– The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. 
A perpendicular line.
– The Concise Standard Dictionary of the English Language. By James Champlin Fernald. Published 1919. 
Perpendicularity.
– The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. 
Hanging or extending in a right line from any point; at right angles to any plane or line; vertical.
– Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. 
A line or plane falling at right angles on another line or surface, or making equal angles with it on each side.
– Newage Dictionary DB 
a straight line at right angles to another line
– Wordnet Dictionary DB 
a cord from which a metal weight is suspended pointing directly to the earth's center of gravity; used to determine the vertical from a given point
– Wordnet Dictionary DB 
a Gothic style in 14th and 15th century England; characterized by vertical lines, a four centered ( Tudor) arch, fan vaulting
– Scrapingweb Dictionary DB 
a Gothic style in 14th and 15th century England; characterized by vertical lines and a four centered ( Tudor) arch and fan vaulting
– Wordnet Dictionary DB 
A line at right angles to the plane of the horizon; a vertical line or direction.
– Newage Dictionary DB 
at right angles to the plane of the horizon or a base line; " a vertical camera angle"; " the monument consists of two vertical pillars supporting a horizontal slab"; " measure the perpendicular height"
– Wordnet Dictionary DB 
At right angles to a given line or surface; as, the line ad is perpendicular to the line bc.
– Newage Dictionary DB 
A line standing at right angles on another line.
– Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.
Quotes for perpendicular:

We can in fact first place the beam of rays of moving positive atomic ions in a plane perpendicular to the axis in which we see the spectral lines emitted by them.
– Johannes Stark 
This seems to be the law of progress in everything we do; it moves along a spiral rather than a perpendicular we seem to be actually going out of the way, and yet it turns out that we were really moving upward all the time.
– Frances E. Willard 
According to well known electrodynamic laws, an electron moving in a magnetic field is acted upon by a force which runs perpendicular to the direction of motion of the electron and to the direction of the magnetic field, and whose magnitude is easily determined.
– Pieter Zeeman 
Now all oscillatory movements of such an electron can be conceived of as being split up into force, and two circular oscillations perpendicular to this direction rotating in opposite directions.
– Pieter Zeeman
Usage examples for perpendicular:

“ The great city expansion in the end will be horizontal rather than perpendicular ”
– The Holy Earth by L. H. Bailey 
“ To verify this, the following observations were made at Ulietea: Day of Water at a stand Mean Time Perpendicular the of rise Month. ”
– A General History and Collection of Voyages and Travels, Volume 16 by Robert Kerr 
“ It was nearly a perpendicular shot. ”
– Wanderings in South America by Charles Waterton 
“ Hooker to return after advancing some miles on this general position, which was about perpendicular to the plank road leading to Fredericksburg, I am not able to say, because, being only a division commander, the facts were not stated to me. ”
– The Campaign of Chancellorsville by Theodore A. Dodge 
“ Prop the pan nearly perpendicular before the blaze. ”
– Camp and Trail by Stewart Edward White 
“ 2184 let A be a section of the moulding, and if the blade or knife is to stand perpendicular as shown at B, Fig. ”
– Modern MachineShop Practice, Volumes I and II by Joshua Rose 
“ Looking down it appeared quite perpendicular and its condition was so changed by the influence of the sun that going down in the same free and easy way that we had climbed up was quite out of the question. ”
– An Impromptu Ascent of Mont Blanc by W. H. Le Mesurier 
“ On the right of the platform, as we approach this building, is a high range of structures, ruined and overgrown with trees, with an immense back wall built on the outer line of the platform, perpendicular to the bottom of the terrace. ”
– Incidents of Travel in Yucatan, Vol. I. by John L. Stephens 
“ The walls are perpendicular and are seldom high enough for a man to stand upright inside the tomb. ”
– Manual Of Egyptian Archaeology And Guide To The Study Of Antiquities In Egypt by Gaston Camille Charles Maspero 
“ He had spent the night leaning against a good sized tree, which his weight had pushed out of the perpendicular ”
– Maiwa's Revenge The War of the Little Hand by H. Rider Haggard 
“ Drives in Beulah township were apt to be rather perpendicular however you took them. ”
– Not Quite Eighteen by Susan Coolidge 
“ I prefer the perpendicular ”
– Frank's Campaign or the Farm and the Camp by Horatio Alger, Jr. 
“ Shoot in the air; let the arrow fall perpendicular on those within fall as the vengeance of the saints falls direct from heaven! ”
– Harold, Complete The Last Of The Saxon Kings by Edward BulwerLytton 
“ The engineer led Frederick to the engine room and down a perpendicular iron ladder. ”
– Atlantis by Gerhart Hauptmann 
“ It was now about noon, and the rays of the sun, which descended almost perpendicular on our heads, were extremely hot and troublesome. ”
– The History of the Life of the Late Mr. Jonathan Wild the Great by Henry Fielding 
“ This is a rather disturbing illusion, particularly for women who are apt to think that perpendicular lines make them appear tall and thin, while horizontal lines have the opposite effect. ”
– Psychotherapy by James J. Walsh 
“ This vallon is short, the walls nearly perpendicular and in some parts scarcely 2 ft. ”
– The South of FranceEast Half by Charles Bertram Black 
“ I can't walk up a perpendicular cliff. ”
– The CockHouse at Fellsgarth by Talbot Baines Reed 
“ Four rates of feed are provided, and the upper wheel can be set at the required angle from a perpendicular while the machine is in motion. ”
– Modern MachineShop Practice, Volumes I and II by Joshua Rose
Rhymes for perpendicular:
 curricular, particular, testicular, vehicular;
 extracurricular;