1530s, of armies, "to retreat, draw back," also, of persons, "to withdraw" to some place, especially for the sake of privacy; from French retirer "to withdraw (something)," from re- "back" (see re-) + Old French tirer "to draw" (see tirade). Related: Retired; retiring.
The sense of "leave one's business or occupation" is by 1660s. The meaning "to leave company and go to bed" is from 1660s. Transitive sense is from 1540s, originally "withdraw, lead back" (troops, etc.); meaning "to remove from active service" is from 1680s. Baseball sense of "to put out" (a batter or team) is recorded by 1874.
1590s, "a private or personal matter, a secret;" c. 1600 as "seclusion, state of being in retirement from company or the knowledge and observation of others," from private (adj.) + abstract noun suffix -cy. Meaning "state of freedom from intrusion or interference" is from 1814. Earlier was privatie (late 14c. as "secret, mystery;" c. 1400 as "a secret, secret deed; solitude, privacy"), from Old French privauté.
<a href="https://www.etymonline.com/word/retiracy">Etymology of retiracy by etymonline</a>
Harper, D. (n.d.). Etymology of retiracy. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/retiracy