1590s, "bulky and strong, characterized by muscle," from brawn + -y (2). Related: Brawniness.
Entries linking to brawny
brawn n.
late 13c., "boar's flesh;" early 14c., "flesh of a muscular part of the body," from Old French braon "fleshy or muscular part, buttock," from Frankish *brado "ham, roast" or some other Germanic source, from Proto-Germanic *bred-on- (source also of Old High German brato "tender meat," German Braten "roast," Old Norse brað "raw meat," Old English bræd "flesh"), from PIE *bhre- "burn, heat," from root *bhreu- "to boil, bubble, effervesce, burn."
The etymological sense is "piece of meat suitable for roasting." "The specific sense 'boar's flesh' is exclusively of English development, and characteristic of English habits" [OED]. The meaning "well-developed muscles, muscular strength" is from 1865.
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.
*bhreu-
also *bhreuə-, *bhreəu-, Proto-Indo-European root meaning "to boil, bubble, effervesce, burn," with derivatives referring to cooking and brewing.
It forms all or part of: barm; barmy; bourn (n.1) "small stream;" braise; bratwurst; brawn; brawny; braze (v.1) "to expose to the action of fire;" brazier; Brazil; bread; breed; brew; broth; broil (v.2) "to quarrel, brawl;" brood; effervesce; effervescence; effervescent; embroil; ferment; fervent; fervid; fervor; imbroglio.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit bhurnih "violent, passionate;" Greek phrear "well, spring, cistern;" Latin fervere "to boil, foam," Thracian Greek brytos "fermented liquor made from barley;" Russian bruja "current;" Old Irish bruth "heat;" Old English breowan "to brew," beorma "yeast;" Old High German brato "roast meat."