'asshole' is a compound of 'ass' and 'hole'; 'ass' (meaning buttocks) traces back to Old English/Proto-Germanic roots for the rear, and 'hole' comes from Old English 'hol' meaning 'opening' or 'hollow'.

'ass' (related to Old English 'ærs'/'ears' meaning 'buttocks') combined with Old English 'hol' produced compounds referring literally to the anatomical opening; the fused vulgar compound 'asshole' is attested in modern English from the late 19th to 20th century and later developed widespread use as an insult.

Originally a literal reference to the anatomical opening ('anus'), over time the primary common use shifted toward a vulgar insult meaning 'an obnoxious or contemptible person.'