Sanity

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late Middle English (in the sense ‘health’): from Latin sanitas ‘health’, from sanus ‘healthy’. Current senses date from the early 17th century.

wiktionary

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sane +‎  -ity, borrowed from Middle French sanité, from Latin sānitas, from  sānus(“healthy”) +  -itās(“-ity”). See  sane,  -ity

etymonline

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sanity (n.)

early 15c., "healthy condition," from Old French sanité "health," from Latin sanitatem (nominative sanitas) "health, sanity," from sanus "healthy; sane" (see sane). Meaning "soundness of mind" is attested from c. 1600.