Bug

Bug as a general name for an insect dates from the 1600s. Bug as an obsession, in expressions like “bitten by a bug” for something or other, dates from the early 19th century. Bug as in a defect, especially in machinery, dates from the late 19th century and derives from insects actually getting into mechanisms and impairing their performance. The modern term “debugging”, an Americanism, derives from this sense but only from the 1940s onwards. Bug as a general term for a microbe or virus is from early 20th century as is bug as in “a bugging device” for listening in on conversations. Bug meaning to annoy is American and dates from the late 1940s.