bug

First attested around 1620 meaning "bedbug," from earlier bugge ("beetle"), from Middle English bugge ("scarecrow, hobgoblin"), possibly tracing to a Celtic root for goblins, a Germanic root meaning "swollen up, thick," or a word related to "buck" describing a goat-shaped spectre.

What began as a word for a haunting, hobgoblin-like fright narrowed into a name for a crawling insect, then leapt into the world of machines: the sense of "technical error" was already in use by the 19th century, well before the famous story of a moth found in an early computer.

The insect sense may have been reinforced by a separate but similarly shaped word, Middle English budde ("beetle"), which is also the ancestor of "bud" — two words that may have grown alongside each other for ages without ever truly merging.