'assert' originates from Latin, specifically the word 'asserere' (frequentative/derived stem), where the prefix 'ad-' meant 'to/toward' and the root 'serere' meant 'to join or put together.'

'assert' changed from Old French 'asserter' (to affirm) and Middle English 'asserten', and eventually became the modern English word 'assert'.

Initially it carried senses related to 'joining' or 'bringing forward' (and by extension 'claiming'), but over time it evolved into its current sense of 'to state or declare firmly.'