WordNet records no synonym and no antonym for stock option. 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.
the right to buy or sell a stock at a specified price within a stated period
a benefit given by a company to an employee in the form of an option to buy stock in the company at a discount or at a fixed price
“stock options are not much use as an incentive if the price at which they can be exercised is out of reach”
Synonyms, antonyms and the broader and narrower relations for stock option come from Princeton University’s WordNet. Full sources and licences.