the.com/sperm whale

means The largest toothed predator alive, a deep-diving whale famous for its massive block-shaped head full of waxy oil, which hunters once prized above almost anything else in the sea.

from The 'sperm' here is a case of mistaken anatomy turned permanent name: the whale's huge head holds a cavity of pale, waxy oil called spermaceti, from Latin sperma ('seed') and ceti ('of the whale'), because early whalers thought the substance was the animal's semen. It wasn't — its real biological role (buoyancy control, acoustic focusing for echolocation) was only understood much later — but by then the name had already been rendered down into lamps, candles, and dictionaries alike, and it stuck.