'axletree' originates from Old English, specifically the compound 'eaxltrēow' (or 'axeltrēow'), where 'eaxl/axel' meant 'axle/shoulder' and 'trēow' meant 'tree/wooden beam'.

'eaxltrēow' passed into Middle English as 'axeltre'/'axeltree' and eventually became the modern English word 'axletree'.

Initially, it referred specifically to a wooden beam or tree-piece used as an axle; over time it came to be used more generally for the axle or shaft on which a wheel turns.