flounder

Concise Oxford English Dictionary © 2008 Oxford University Press:
flounder1

▶verb

• 1 stagger clumsily in mud or water.

• 2 have trouble doing or understanding something.

– derivatives
flounderer noun.

– origin C16: perh. a blend of founder3 and blunder, or perh. symbolic.

usage: On the confusion of flounder with founder, see founder3.

Concise Oxford English Dictionary © 2008 Oxford University Press:
flounder2

▶noun a small flatfish that typically occurs in shallow coastal water. [Platichthys flesus and other species.]

– origin ME: from OFr. flondre, prob. of Scand. origin.