Definition of: flea

(fiē) noun
1. A wingless insect (order Siphonaptera), parasitic upon a mammal or a bird, and having a compressed body, limbs adapted for leaping, and a head armed with piercing mandibles and a suctorial proboscis. For illustration see under INSECT (injurious). ♦ Collateral adjective: pulicene.
2. One of several small beetles or crustaceans that jump like fleas, as a beach flea or sand hopper. ♦ Homophonerer: flee. [OE flēa. Akin to FLEE.]
—a flea in one's (or the) ear
A warning; caution; sometimes, an irritating reply or rebuff.