'atilt' originates from the Old English/early Middle English prefix 'a-' (meaning 'on, in, at') added to the word 'tilt' (Middle English 'tilten'/'tilt'), where the prefix 'a-' meant 'on' or 'in the state of' and 'tilt' meant 'to lean, slant, or thrust.

'atilt' appears in Middle English as forms like 'a-tilt' and developed as a fused adjective/adverb meaning 'in a tilted state', eventually stabilizing in modern English as 'atilt'.

Initially it meant 'in a state of tilting' and over time has retained that basic sense, used to describe things that are slanted or off-level.