WordNet records no synonym and no antonym for manhattan project. 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 former United States executive agency that was responsible for developing atomic bombs during World War II
code name for the secret United States project set up in 1942 to develop atomic bombs for use in World War II
Synonyms, antonyms and the broader and narrower relations for manhattan project come from Princeton University’s WordNet. Full sources and licences.