1690s, regarded as a softened variant of flappy, which is recorded in the sense of "softly fleshy" from 1590s; see flap (n.). Related: Flabbily; flabbiness.
Entries linking to flabby
flap n.
mid-14c., flappe "a blow, slap, buffet," probably imitative of the sound of striking. Sense of "device for slapping or striking" is from early 15c. Meaning "something that hangs down" is first recorded 1520s, probably from flap (v.). Sense of "motion or noise like a bird's wing" is 1774; meaning "disturbance, noisy tumult" is 1916, British slang.
flab n.
"fat, flabbiness," 1951, back-formation from flabby.