'unpoetically' was formed in Modern English by adding the adverbial suffix '-ly' to the adjective 'unpoetic', itself created by prefixing the negative 'un-' to 'poetic'. 'poetic' ultimately comes from Latin 'poeticus', from Greek 'poietikos' (from 'poiein') where 'poiein' meant 'to make'.

'poetic' entered English via Latin 'poeticus' and Old French (e.g. 'poetique'), becoming Middle English 'poetic'. The productive negative prefix 'un-' (Old English and later) produced 'unpoetic' in post-medieval English, and the suffix '-ly' formed the adverb 'unpoetically'.

Originally related to 'poet' or 'poetry' — 'of or relating to poets' — 'poetic' broadened to mean 'having qualities of poetry; expressive or beautiful'. 'Unpoetically' therefore evolved to mean 'in a way that lacks those poetic qualities'.