'wanly' originates from Old English, specifically the adjective 'wann', where the root meant 'dark, gloomy' and the adverbial suffix '-ly' formed the adverb.

'wann' in Old English developed into Middle English 'wan', and the modern adverb 'wanly' arose by adding the suffix '-ly' to form 'in a wan manner'.

Initially, the root conveyed a sense of 'dark or gloomy', but over time it shifted toward the meaning 'pale or lacking color' and then to 'pale and weak' in the adverbial use.