1520s, from whirl (v.) + pool (n.1). Old English had hwyrfepol and wirfelmere.
Entries linking to whirlpool
whirl v.
c. 1300, probably from Old Norse hvirfla "to go round, spin," related to hvirfill "circle, ring, crown," and to Old English hweorfan "to turn" (see wharf). Related: Whirled; whirling. Whirlybird "helicopter" is from 1951.
pool n.1
"small body of standing water," Old English pol "small body of water; deep, still place in a stream," from Proto-West Germanic *pōl- (source also of Old Frisian and Middle Low German pol, Dutch poel, Old High German pfuol, German Pfuhl "pool, puddle"), which is of uncertain origin, perhaps a substratum word [Boutkan]. As a short form of swimming pool it is recorded from 1901. Pool party "party at a swimming pool" is by 1965.