WordNet records no synonym and no antonym for cleat. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
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.
a metal or leather projection (as from the sole of a shoe); prevents slipping
a fastener (usually with two projecting horns) around which a rope can be secured
a strip of wood or metal used to strengthen the surface to which it is attached
provide with cleats
“cleat running shoes for better traction”
Synonyms, antonyms and the broader and narrower relations for cleat come from Princeton University’s WordNet. Full sources and licences.