'asseverate' originates from Latin, specifically the verb 'asserverare' (or 'asseverare'), formed from the prefix 'ad-' (expressing 'to, toward') and 'severus' meaning 'serious'.

'asseverare' (Late Latin) passed into English via learned borrowings in the 17th century as 'asseverate', retaining the Latinate form and meaning.

Initially it meant 'to make serious or earnest declaration' and over time evolved into the current sense of 'to assert or affirm positively and earnestly', a meaning largely preserved.