What is the X in X-mas?
"thorny shrub, heath," 1540s, variant of Middle English brere, from Old English brer (Anglian), brær (West Saxon) "brier, bramble, prickly bush," 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.
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-Romance *brucaria, from *brucus "heather," from Gaulish (cf. Breton brug "heath," Old Irish froech). Form altered in English by influence of brier (n.1).
This word occurs frequently, and is the translation of several different terms. (1.) Micah 7:4, it denotes a species of thorn shrub used for hedges. In Prov. 15:19 the word is rendered "thorn" (Heb. _hedek_, "stinging"), supposed by some to be what is called the "apple of Sodom" (q.v.). (2.) Ezek. 28:24, _sallon'_, properly a "prickle," such as is found on the shoots of the palm tree. (3.) Isa. 55:13, probably simply a thorny bush. Some, following the Vulgate Version, regard it as the "nettle." (4.) Isa. 5:6; 7:23-25, etc., frequently used to denote thorny shrubs in general. In 10:17; 27:4, it means troublesome men. (5.) In Heb. 6:8 the Greek word (tribolos) so rendered means "three-pronged," and denotes the land caltrop, a low throny shrub resembling in its spikes the military "crow-foot." Comp. Matt. 7:16, "thistle."