Latin 'recludere' meant 'to open' — monks reversed it to 'shut away.' English inherited the flipped meaning.
A person who lives in seclusion, withdrawn from society; favouring or characterized by seclusion.
From Old French 'reclus' (shut up, enclosed), from Latin 'reclūsus,' past participle of 'reclūdere.' In Classical Latin, 'reclūdere' meant 'to open, to unclose' (re- reversing the closing). However, in Late and Medieval Latin, the meaning shifted to 'to shut away, to enclose' (re- as an intensifier), particularly in monastic contexts where a 'reclūsus' was a person sealed into a cell for
In Classical Latin, 'reclūdere' meant 'to OPEN' — the prefix 're-' reversed the closing. But Medieval monks used it to mean 'to shut away' — re- as an intensifier, meaning to close thoroughly. English inherited the medieval meaning, so 'recluse' means the opposite of what the original Latin verb would suggest.