before a vowel, brachi-, word-forming element meaning "arm, of the upper arm, pertaining to the upper arm and," from Latinized form of Greek brakhion "arm," perhaps originally "upper arm," literally "shorter," from brakhys "short" (from PIE root *mregh-u- "short"), in contrast to the longer forearm.
Entries linking to brachio-
*mregh-u-
Proto-Indo-European root meaning "short."
It forms all or part of: abbreviate; abbreviation; abridge; amphibrach; brace; bracelet; brachio-; brachiopod; brachiosaurus; brachy-; brassiere; breviary; brevity; brief; brumal; brume; embrace; merry; mirth; pretzel; vambrace.
It is the hypothetical source of/evidence for its existence is provided by: Greek brakhys "short;" Latin brevis "short, low, little, shallow;" Old Church Slavonic bruzeja "shallow places, shoals;" Gothic gamaurgjan "to shorten."
brace n.
early 14c., "piece of armor for the arms," also "thong, strap for fastening," from Old French brace "arms," also "length measured by two arms" (12c., Modern French bras "arm, power;" brasse "fathom, armful, breaststroke"), from Latin bracchia, plural of bracchium "an arm, a forearm," from Greek brakhion "an arm" (see brachio-).
The meaning "that which holds two or more things firmly together" (on the notion of clasping arms) is from mid-15c. Hence the word is applied to various devices for fastening and tightening. The meaning "a prop, support," especially in architecture, is from 1520s. Of dogs, ducks, pistols, etc., "a couple, a pair" from c. 1400.
Braces is from 1798 as "straps passing over the shoulders to hold up the trousers;" from 1945 as "wires for straightening the teeth."