"thorny shrub, heath," 1540s, a variant of Middle English brere, from Old English brer (Anglian), brær (West Saxon) "brier, bramble, prickly bush," which is of unknown origin. Briar is the most recent variant (c. 1600). Originally used of prickly, thorny bushes in general, now mostly restricted to wild rose bushes (sweet briar). Used figuratively (in plural) for "troubles" from c. 1500. French bruyère "heath plant" (source of brier (n.2)) is considered to be unrelated.
contrive v.
early 14c., controve, contreve, "to invent, devise, plan;" late 14c., "to manage by a plan or scheme," from Old French controver (Modern French controuver) "to find out, contrive, imagine," from Late Latin contropare "to compare" (via a figure of speech), from an assimilated form of Latin com "with, together" (see con-) + tropus "song, musical mode," from Greek tropos "figure of speech" (from PIE root *trep- "to turn").
Sense evolution (in French) was from "invent with ingenuity" to "invent falsely." Spelling in English was altered by the same unexplained 15c. sound change that also affected briar, friar, choir. Related: Contrived; contriving.
sweet-briar n.
"eglantine," 1530s, from sweet (adj.) + briar (n.).