WordNet records no synonym and no antonym for alphabet soup. 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 confusing assortment
“Roosevelt created an alphabet soup of federal agencies”
soup that contains small noodles in the shape of letters of the alphabet
Synonyms, antonyms and the broader and narrower relations for alphabet soup come from Princeton University’s WordNet. Full sources and licences.