WordNet records no synonym and no antonym for crutch. 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 wooden or metal staff that fits under the armpit and reaches to the ground; used by disabled person while walking
anything that serves as an expedient
“he uses drugs as a psychological crutch”
Synonyms, antonyms and the broader and narrower relations for crutch come from Princeton University’s WordNet. Full sources and licences.