circuit has 7 distinct synonyms spread across 5 of its 8 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.
an electrical device that provides a path for electrical current to flow
a journey or route all the way around a particular place or area
“they took an extended tour of Europe”
an established itinerary of venues or events that a particular group of people travel to
“she's a familiar name on the club circuit”
the boundary line encompassing an area or object
“he had walked the full circumference of his land”
(law) a judicial division of a state or the United States (so-called because originally judges traveled and held court in different locations); one of the twelve groups of states in the United States that is covered by a particular circuit court of appeals
movement once around a course
“he drove an extra lap just for insurance”
make a circuit
“They were circuiting about the state”
Synonyms, antonyms and the broader and narrower relations for circuit come from Princeton University’s WordNet. Full sources and licences.