c. 1200, "person shut up or withdrawn from the world and secular living for purposes of religious meditation," originally and especially as a member of a religious community, from Old French reclus (fem. recluse) "hermit, recluse," also "confinement, prison; convent, monastery," noun use of reclus (adj.) "shut up," from Late Latin reclusus, past participle of recludere "to shut up, enclose" (but in classical Latin "to throw open"), from Latin re-, here perhaps an intensive prefix (see re-), + claudere "to shut" (see close (v.)).
Also in part via Medieval Latin nouns reclusus, reclusa. By late 17c. in the secular and softened sense of "one who lives a retired life and mixes little in society." Middle English also had a verb reclusen "to shut up (in some place), confine," and the past-participle adjective reclused "living in seclusion" (c. 1200). Recluse as an adjective meaning "shut up or apart from the world" is attested from early 13c. Also in Middle English was reclusion "state of retirement from the world" (c. 1400), from Medieval Latin reclusionem.