late 14c., "low, of little height," from Old French bas "low, lowly, mean," from Late Latin bassus "thick, stumpy, low" (used only as a cognomen in classical Latin, humilis being there the usual word for "low in stature or position"), which is of uncertain origin, possibly from Oscan, or Celtic, or related to Greek basson, comparative of bathys "deep."

The meaning "low on the social scale" is from late 15c.; that of "low in the moral scale" is attested by 1530s in English. The meaning "befitting an inferior person or thing, unworthy" is from 1590s. Base metals (c. 1600) were worthless in contrast to noble or precious metals. Related: Basely.

early 15c., "embarrassment, dread, fear," from abase + -ment. Sense of "action of lowering in price" is mid-15c.; "action of lowering in rank" is 1560s; "condition of being abased" is from 1610s.