'sententious' originates from Latin, specifically the word 'sententiosus', where 'sententia' meant 'opinion, judgment, thought'.

'sententiosus' in Late Latin passed into Old French / Middle French as words like 'sentencieux' and then entered English in the form 'sententious' in the 16th century; the adverb 'sententiously' is formed later by adding the adverbial suffix '-ly' to the adjective.

Initially related to 'having or showing opinions/judgments' (from 'sententia'), the word's sense shifted toward 'pithy, moralizing, or aphoristic expression', which is reflected in modern uses of 'sententious' and 'sententiously'.