solitary adj.

"single, alone in its kind; one and only, singular, unique; having no husband or wife, in an unmarried state; celibate," late 14c., from Old French soul "only, alone, just," from Latin solus "alone, only, single, sole; forsaken; extraordinary," a word of unknown origin, perhaps related to se "oneself," from PIE reflexive root *swo- (for which see so).

c. 1500, "widow;" 1716, "person who lives in solitude, recluse," from French solitaire, from Latin adjective solitarius "alone, lonely, isolated" (see solitary). The sense of "a precious stone set by itself" is from 1727. The meaning "card game played by one person" (usually involving bringing shuffled cards into sequence) is attested by 1746.

Solitarian "a recluse" is by 1650s; solitary (n.) was in Middle English as "hermit, religious recluse" (late 14c.), "person without companions" (early 15c.). Latin solitarius in Late Latin also was a noun, "anchorite."