WordNet records no synonym and no antonym for paper tiger. 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 nature of a person or organization that appears powerful but is actually powerless and ineffectual
“he reminded Mao that the paper tiger had nuclear teeth”
Synonyms, antonyms and the broader and narrower relations for paper tiger come from Princeton University’s WordNet. Full sources and licences.