bug / bəg/ • n. 1. a small insect. ∎ inf. a harmful microorganism, as a bacterium or virus. ∎  an illness caused by such a microorganism. ∎  fig., inf. an enthusiastic, almost obsessive, interest in something: they caught the sailing bug. 2. (also true bug) Entomol. an insect of a large order (Hemiptera) distinguished by having mouthparts that are modified for piercing and sucking. 3. a concealed miniature microphone, used for surveillance. 4. an error in a computer program or system.• v. (bugged , bugging ) [tr.] 1. (often be bugged) conceal a miniature microphone in (a room, telephone, etc.) in order to monitor or record someone's conversations. ∎  record or monitor (a conversation) in this way. 2. inf. annoy or bother (someone). PHRASAL VERBS: bug off inf. go away.bug out inf. 1. leave quickly. 2. chiefly fig. bulge outward.

bug1 †object of dread. XIV. The earliest of several words of similar form and meaning, the connections of which are obscure; viz. †bog, †boggard, (dial.) bogle, bogle-bo, BUGABOO, BUGBEAR, and the more recent BOGEY. Comparison with W. bwg, bwgan ghost, hobgoblin, bwgwl fear, threat, is inevitable, but it is uncertain how these forms are related.

bug Any member of the insect order Hemiptera, although in the USA any insect is commonly called a bug. True bugs are flattened insects that undergo gradual or incomplete metamorphosis, have two pairs of wings and use piercing and sucking mouthparts. Most feed on plant juices, such as the greenfly, although a number attack animals and are carriers of disease.

bug An error in a program or system. The word is usually used to mean a localized implementation error rather than, say, an error introduced at the requirements or system-design stage. See also debugging.

bug Bug Bible a name given to versions of the English Bible ( Coverdale's and Matthew's) in which the words in Psalm 91:5 are translated, ‘thou shalt not be afraid for any bugs by night’.
bug-eyed monster an extra-terrestrial monster with bulging eyes.