host (n.1) Look up host at Dictionary.com
"person who receives guests," late 13c., from Old French hoste "guest, host, hostess, landlord" (12c., Modern French hôte), from Latin hospitem (nominative hospes) "guest, host," literally "lord of strangers," from PIE *ghostis- "stranger" (cognates: Old Church Slavonic gosti "guest, friend," gospodi "lord, master;" see guest). The biological sense of "animal or plant having a parasite" is from 1857.
host (n.2) Look up host at Dictionary.com
"multitude" mid-13c., from Old French host "army" (10c.), from Medieval Latin hostis "army, war-like expedition," from Latin hostis "enemy, foreigner, stranger," from the same root as host (n.1). Replaced Old English here, and in turn has been largely superseded by army. The generalized meaning of "large number" is first attested 1610s.
host (n.3) Look up host at Dictionary.com
"body of Christ, consecrated bread," c.1300, from Latin hostia "sacrifice," also "the animal sacrificed," applied in Church Latin to Christ; probably ultimately related to host (n.1) in its root sense of "stranger, enemy."
host (v.) Look up host at Dictionary.com
"to serve as a host," early 15c., from host (n.1). Related: Hosted; hosting.