'lightheadedly' originates from English, specifically formed from the adjective 'lightheaded' plus the adverbial suffix '-ly', where 'light' originally meant 'not heavy' and 'head' referred to 'head'.

'lightheaded' developed in modern English as a compound of 'light' + 'headed' (literally 'having a light head') and later took the suffix '-ly' to form the adverb 'lightheadedly'.

Initially the components suggested a literal 'light (not heavy) head', but over time the compound came to describe a subjective sensation of dizziness or faintness; the adverb now means 'in a dizzy or faint way'.