Acrostic \A*cros"tic\, n. [Gr. ?; ? extreme + ? order, line, verse.]

1. A composition, usually in verse, in which the first or the last letters of the lines, or certain other letters, taken in order, form a name, word, phrase, or motto.

2. A Hebrew poem in which the lines or stanzas begin with the letters of the alphabet in regular order (as Psalm cxix.). See Abecedarian.

Double acrostic, a species of enigma

Source: Webster's Revised Unabridged Dictionary (1913)
 

Acrostic \A*cros"tic\, Acrostical \A*cros"tic*al\, n. Pertaining to, or characterized by, acrostics.

Source: Webster's Revised Unabridged Dictionary (1913)