'barf' originates from American English slang, probably from an imitative or onomatopoeic source; recorded in the early 20th century.

'barf' appeared in U.S. slang in the early 1900s and retained the same form 'barf' into modern English usage as an informal term for 'vomit'.

Initially it meant 'to vomit' (or the sound/idea of vomiting) and over time it has remained largely the same in meaning, though it has stayed informal and slangy.