large marine snail, Old English weoloc, wioloc, from Proto-Germanic *weluka- (cf. Middle Dutch willoc, Dutch wulk), perhaps from PIE root *wel- "to turn, revolve" (see volvox; cf. also volute). The spelling with wh- dates from 15c.
whelk (wělk)n. An inflamed swelling, such as a pimple or pustule.