WordNet records no synonym and no antonym for catwalk. 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.
narrow platform extending out into an auditorium
“models displayed clothes on a catwalk at the fashion show”
narrow pathway high in the air (as above a stage or between parts of a building or along a bridge)
Synonyms, antonyms and the broader and narrower relations for catwalk come from Princeton University’s WordNet. Full sources and licences.