mansion

Mansion comes from Middle English mansioun, borrowed from Anglo-Norman mansion/mansiun, which traces to Latin mānsiō, meaning 'dwelling, stopping-place.' That Latin noun grew from the past participle stem of manēre, 'to stay.'

The word's root sense was simply a stopping-place where one stays, not necessarily anything grand — the grandeur is a later association.

By surface analysis, mansion breaks down as manse plus the suffix -ion, tying it to the word 'manse,' another word for a dwelling place, particularly a clergyman's house.