Onerous \On"er*ous\, a. [L. onerosus, fr. onus, oneris, a load, burden: cf. F. on['e]reux.]

Burdensome; oppressive. "Too onerous a solicitude." --I. Taylor. [1913 Webster]

Onerous cause (Scots Law), a good and legal consideration; -- opposed to gratuitous. [1913 Webster]

Source: The Collaborative International Dictionary of English v.0.48
 

70 Moby Thesaurus words for "onerous": Herculean, annoying, arduous, arduously, backbreaking, besetting, bothersome, burdensome, burdensomely, crushing, cumbersome, cumbrous, demanding, difficult, difficultly, effortful, encumbering, exacting, exhausting, exigent, forced, grievous, grinding, grueling, hampering, hard, hard-earned, hard-fought, hardly, harsh, heavy, heavy-handed, hefty, impedimental, impeding, impeditive, incumbent, irksome, killing, labored, laborious, laboriously, lumpish, massive, onerously, operose, oppressive, overburdensome, painful, plaguey, ponderous, punishing, strained, strenuous, superincumbent, taxing, toilsome, toilsomely, tough, troublesome, trying, tyrannous, unruly, unwieldy, uphill, vexatious, wearing, wearisome, wearying, weighty

Source: Moby Thesaurus II by Grady Ward, 1.0
 

onerous adj : not easily borne; wearing; "the burdensome task of preparing the income tax return"; "my duties weren't onerous; I only had to greet the guests"; "a taxing schedule" [syn: burdensome, taxing]

Source: WordNet (r) 2.0
 

Onerous \On"er*ous\, a. [L. onerosus, fr. onus, oneris, a load, burden: cf.F. on['e]reux.]

Burdensome; oppressive. ``Too onerous a solicitude.'' --I. Taylor.

Onerous cause (Scots Law), a good and legal consideration; -- opposed to gratuitous.

Source: Webster's Revised Unabridged Dictionary (1913)