relay has 2 distinct synonyms spread across 2 of its 7 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. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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.
the act of passing something along from one person or group to another
“the relay was successful”
a crew of workers who relieve another crew
a fresh team to relieve weary draft animals
Synonyms, antonyms and the broader and narrower relations for relay come from Princeton University’s WordNet. Full sources and licences.
a race between teams; each member runs or swims part of the distance
electrical device such that current flowing through it in one circuit can switch on and off a current in a second circuit
pass along
“Please relay the news to the villagers”