WordNet records no synonym and no antonym for outsole. It is the only member of its synset, 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.
the outer sole of a shoe or boot that is the bottom of the shoe and makes contact with the ground
Synonyms, antonyms and the broader and narrower relations for outsole come from Princeton University’s WordNet. Full sources and licences.