'reclusive' originates from Latin, specifically the past participle 'reclusus' (from 'recludere'), where 're-' meant 'back' and 'claudere'/'cludere' (from which 'cludere' is derived) meant 'to shut'.

'reclusus' (Latin) passed into Medieval Latin as 'reclusivus' and via Middle English became 'reclusive'; the adverbial form 'reclusively' was formed by adding the -ly suffix to the adjective.

Initially it referred to being 'shut back or shut away' (physically enclosed); over time it came to denote a voluntary withdrawal from society and the modern sense of 'preferring solitude'.