host has 7 distinct synonyms spread across 5 of its 11 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is parasite.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
an animal or plant that nourishes and supports a parasite; it does not benefit and is often harmed by the association
a person who acts as host at formal occasions (makes an introductory speech and introduces other speakers)
any organization that provides resources and facilities for a function or event
“Atlanta was chosen to be host for the Olympic Games”
(medicine) recipient of transplanted tissue or organ from a donor
a technical name for the bread used in the service of Mass or Holy Communion
be the host of or for
“We hosted 4 couples last night”
Synonyms, antonyms and the broader and narrower relations for host come from Princeton University’s WordNet. Full sources and licences.