The story
From Saxidomus giganteus (butter clam), from which it was first isolated + toxin.
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: A neurotoxin, produced by some dinoflagellates, associated with red tides, that can accumulate in molluscs and cause subsequent food poisoning in humans Full definition →
From Saxidomus giganteus (butter clam), from which it was first isolated + toxin.
Etymology from Wiktionary, CC BY-SA 4.0.