'aswoon' originates from the prefix 'a-' (an English prefix meaning 'in' or 'on', ultimately from Old English usage) combined with the word 'swoon' (English).

'aswoon' appeared in Middle English as 'aswoun' or 'aswounen' (formed from 'a-' + 'swoun'/'swonen'), and over time the spelling simplified to the modern form 'aswoon'.

Initially it simply meant 'in a swoon' or 'in a faint' and that core sense has been retained; the word has become archaic in modern usage.