A river flowing northwest 450 miles between Belarus and Poland.

A river in Ukraine (Southern Bug), flowing 530 miles to the Dnieper estuary.

(US, slang) A Volkswagen Beetle car.

(slang) A Bugatti car.

(entomology) An insect of the order Hemiptera (the “true bugs”).

Any of various species of marine or freshwater crustaceans; e.g. a Moreton Bay bug, mudbug.

(informal) Any insect, arachnid, or other terrestrial arthropod that is a pest.

(US) Any insect, arachnid, myriapod or entognath.

(chiefly computing and engineering jargon) A problem that needs fixing.

A contagious illness, or a pathogen causing it.

(informal) An enthusiasm for something; an obsession.

(informal) A keen enthusiast or hobbyist.

A concealed electronic eavesdropping or intercept device.

A small and usually invisible file (traditionally a single-pixel image) on a World Wide Web page, primarily used to track users.

(broadcasting) A small, usually transparent or translucent image placed in a corner of a television program to identify the broadcasting network or cable channel.

(aviation) A manually positioned marker in flight instruments.

A semi-automated telegraph key.

(chiefly LGBT, "the bug") HIV.

(poker) A limited form of wild card in some variants of poker.

(paleontology, slang) A trilobite.

(slang, US, horse-racing) An asterisk denoting an apprentice jockey's weight allowance.

(slang, US, horse-racing, by extension) A young apprentice jockey.

(printing) Synonym of union bug.

(gambling, slang) A small piece of metal used in a slot machine to block certain winning combinations.

(gambling, slang) A metal clip attached to the underside of a table, etc. to hold hidden cards, as a form of cheating.

(informal, transitive) To annoy.

(informal, intransitive) To act suspiciously or irrationally, especially in a way that annoys others.

(transitive) To install an electronic listening device or devices in.