WordNet records no synonym and no antonym for lewis and clark expedition. 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.
an expedition sent by Thomas Jefferson to explore the northwestern territories of the United States; led by Meriwether Lewis and William Clark; traveled from St. Louis to the mouth of the Columbia River from 1803 to 1806
Synonyms, antonyms and the broader and narrower relations for lewis and clark expedition come from Princeton University’s WordNet. Full sources and licences.