"thorny shrub, heath," 1540s, variant of Middle English brere, from Old English brer (Anglian), br?r (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. Used figuratively (in plural) for "troubles" from c. 1500.
brier (n.2)
type of tobacco pipe introduced to England c. 1859 and made from the root of a certain shrub, 1868, from French bruyère "heath plant," from Old French bruiere "heather, briar, heathland, moor" (12c.), from Gallo-Roman *brucaria, from *brucus "heather," from Gaulish (compare Breton brug "heath," Old Irish froech). Form altered in English by influence of brier (n.1).