WordNet records no synonym and no antonym for sell short. 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.
sell securities or commodities or foreign currency that is not actually owned by the seller, who hopes to cover (buy back) the sold items at a lower price and thus to earn a profit
underestimate the real value or ability of
“Don't sell your students short--they are just shy and don't show off their knowledge”
Synonyms, antonyms and the broader and narrower relations for sell short come from Princeton University’s WordNet. Full sources and licences.