'boner' originates from English, specifically the word 'bone' with the agentive/derivational suffix '-er', where 'bone' originally meant 'a hard part of an animal or human skeleton.'

'bone' comes from Old English 'bān' meaning 'bone'; over time the Modern English noun 'bone' produced derived forms such as 'boner' in slang use (U.S. student and colloquial speech from the late 19th to early 20th century).

Initially related to 'bone' as the literal skeletal element, the derived slang 'boner' came to mean 'a conspicuous blunder' (late 19th/early 20th c.) and later also acquired the vulgar sense 'an erection' in 20th-century colloquial English.