WordNet records no synonym and no antonym for pannier. 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.
either of a pair of bags or boxes hung over the rear wheel of a vehicle (as a bicycle)
a large basket (usually one of a pair) carried by a beast of burden or on by a person
set of small hoops used to add fullness over the hips
Synonyms, antonyms and the broader and narrower relations for pannier come from Princeton University’s WordNet. Full sources and licences.