'athort' originates from Middle English, specifically the word 'athort' (also attested as 'athwart'), where the prefix 'a-' meant 'on' or 'in' and the root element (from Old English/Old Norse) meant 'across' or 'crosswise'.

'athort' developed via Middle English forms such as 'athort'/'athwart' from Old English expressions (compare Old English 'on þweorh' meaning 'on the transverse') and related Old Norse/Old English roots (compare Old Norse 'þvert'). Over time these forms yielded the modern archaic/dialectal 'athort'.

Initially it meant 'on or across' (a spatial relation); this core meaning has largely been preserved, though the word became less common and is now chiefly archaic or dialectal in usage meaning 'across' or 'crosswise'.