"mental inclination, natural state of the mind as disposed toward something," 1570s, probably from earlier literal sense "condition of being deflected or turned" (1530s), from bent (adj.) "not straight" (q.v.).
"stiff grass," Old English beonet (attested only in place names), from West Germanic *binut- "rush, marsh grass" (source also of Old Saxon binet, Old High German binuz, German Binse "rush, reed"), which is of unknown origin. An obsolete word, but surviving in place names (such as Bentley, from Old English Beonet-leah; and Bentham).
The verdure of the plain lies buried deep
Beneath the dazzling deluge; and the bents,
And coarser grass, upspearing o'er the rest,
Of late unsightly and unseen, now shine
Conspicuous, and, in bright apparel clad
And fledg'd with icy feathers, nod superb.
[Cowper, "The Winter-Morning Walk," from "The Task"]
"not straight, curved like a strung bow," late 14c. (earlier ibent, c. 1300), from past participle of bend (v.). Meaning "turned or inclined in some direction" is from 1530s, probably as a translation of Latin inclinatio. Meaning "directed in a course" is from 1690s.
Used throughout 20c. in various slang and underworld senses: "criminal; illegal; stolen; corrupted; broken; insane; homosexual;" compare slang uses of crooked. Figurative phrase bent out of shape "extremely upset" is 1960s U.S. Air Force and college student slang.