popple
Choppy water; the motion or sound of agitated water (as from boiling or wind).
Commander Birch was a trifle uneasy when he found there was more than a popple on the sea; it was, in fact, distinctly choppy.
Where it comes from
From Middle English poplen, possibly from Middle Dutch, of imitative origin.
Adapted from the Wiktionary entry popple (CC BY-SA 4.0).