expedition has 11 distinct synonyms spread across 3 of its 5 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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 military campaign designed to achieve a specific objective in a foreign country
an organized group of people undertaking a journey for a particular purpose
“an expedition was sent to explore Mars”
a journey organized for a particular purpose
a journey taken for pleasure
“many summer excursions to the shore”
the property of being prompt and efficient
“it was done with dispatch”
Synonyms, antonyms and the broader and narrower relations for expedition come from Princeton University’s WordNet. Full sources and licences.