buxom (adj.) Look up buxom at Dictionary.com
late 12c., buhsum "humble, obedient," from Old English bugen "to bow" (from Proto-Germanic *bugan-, from PIE root *bheug- "to bend") + -som (see -some (1)), for a total meaning "capable of being bent." Meaning progressed from "compliant, obliging," through "lively, jolly," "healthily plump, vigorous," to (in women, and perhaps influenced by lusty) "plump, comely" (1580s). In Johnson [1755] the primary meaning still is "obedient, obsequious."

Used often of breasts, and by 1950s it had begun to be used more narrowly for "bosomy" and could be paired with slim (adj.). Dutch buigzaam, German biegsam "flexible, pliable" hew closer to the original sense of the English cognate.