'attently' originates from Middle English, specifically the word 'attent', ultimately from Latin 'attentus' (past participle of 'attendere'), where 'ad-' meant 'to/toward' and 'tendere' meant 'to stretch/extend'.

'attently' changed from Middle English 'attent' (an adjective) with the adverbial suffix '-ly' added, tracing back through Old French forms to Latin 'attentus' and the verb 'attendere'.

Initially related to 'attend' (to stretch toward, to direct one's mind), it evolved into the sense 'to give attention' and as an adverb came to mean 'with attention' (now archaic or literary).