"person who receives guests," especially for pay, late 13c., from Old French oste, hoste "guest, host, hostess, landlord" (12c., Modern French hôte), from Latin hospitem (nominative hospes) "guest, stranger, sojourner, visitor (hence also 'foreigner')," also "host; one bound by ties of hospitality."
This appears to be from PIE *ghos-pot-, a compound meaning "guest-master" (compare Old Church Slavonic gospodi "lord, master," literally "lord of strangers"), from the roots *ghos-ti- "stranger, guest, host" and *poti- "powerful; lord." The etymological notion is of someone "with whom one has reciprocal duties of hospitality" [Watkins]. The biological sense of "animal or plant having a parasite" is from 1857.
It replaced Old English here (see harry (v.)), and in turn has been largely superseded by army. The generalized meaning of "large number" is first attested 1610s. The Latin h- was lost in Old French, then restored in Old French and Middle English spelling, and in modern English also in pronunciation. Lord of Hosts translates Hebrew Jehovah Ts'baoth (which appears more than 260 times throughout the Bible) and seems to refer to both heavenly (angelic) and earthly hosts.
former title of appointed Ottoman governors of Moldavia and Wallachia, 1680s, from Old Church Slavonic gospodi "lord, master," literally "lord of strangers," from gosti "guest, friend," from PIE *ghostis- "stranger" (from root *ghos-ti- "stranger, guest, host"); second element from PIE root *poti- "powerful; lord." Compare host (n.1).
"kind and cordial to strangers or guests," 1560s, from French hospitable, which is formed as if from a Medieval Latin hospitabilis, from the stem of Latin hospitari "be a guest," from hospes (genitive hospitis) "guest" (see host (n.1)). The Latin adjective was hospitalis, but this became a noun in Old French and entered English as hospital. Related: Hospitably.