WordNet records no synonym and no antonym for stroma. 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 mass of fungal tissue that has spore-bearing structures embedded in it or on it
the dense colorless framework of a chloroplast
the supporting tissue of an organ (as opposed to parenchyma)
Synonyms, antonyms and the broader and narrower relations for stroma come from Princeton University’s WordNet. Full sources and licences.