FLOUN'DER, noun A flat fish of the genus Pleuronectes. FLOUN'DER, verb intransitive [This seems to be allied to flaunt and flounce.] To fling the limbs and body, as in making efforts to move; to struggle as a horse in the mire; to roll, toss and tumble.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI