bug (Noun) — General term for any insect or similar creeping or crawling invertebrate.
bug (Noun) — A fault or defect in a computer program, system, or machine.
bug (Noun) — A small hidden microphone; for listening secretly.
bug (Noun) — Insects with sucking mouthparts and forewings thickened and leathery at the base; usually show incomplete metamorphosis.
bug (Noun) — A minute life form (especially a disease-causing bacterium); the term is not in technical use.
bug (Verb) — Annoy persistently. ex. "The children bugged the boy because of his stammer"
bug (Verb) — Secretly listen in on a communication channel (esp. a telephone) in order to get information. ex. "Is this hotel room bugged?"
bug (Verb) — Put in place electronic eavesdropping equipment. ex. "his house is bugged"