Definition of earworms:
(n) :
A tune that keeps replaying in one's head or that one keeps thinking about, especially if unwanted.
(n) :
(archaic) An earwig (“insect of the order Dermaptera”).
(n) :
(originally US) Ellipsis of corn earworm (“larva of the moths Helicoverpa zea (syn. Heliothis zea) and Helicoverpa armigera, which are agricultural pests”). [The large striped yellow-headed larva of moths of species Helicoverpa zea (syn. Heliothis zea) and Helicoverpa armigera, especially destructive to corn, tomatoes, tobacco, and cotton bolls.]