 The name sperm whale is a clip of spermaceti whale . Spermaceti , originally mistakenly identified as the whales ' semen , is the semi @-@ liquid , waxy substance found within the whale 's head ( see below ) . The sperm whale is also known as the " cachalot " , which is thought to derive from the archaic French for " tooth " or " big teeth " , as preserved for example in cachau in the Gascon dialect ( a word of either Romance or Basque origin ) . The etymological dictionary of Corominas says the origin is uncertain , but it suggests that it comes from the Vulgar Latin cappula , plural of cappulum , " sword hilt " . The word cachalot came to English via French from Spanish or Portuguese cachalote , perhaps from Galician / Portuguese cachola , " big head " . The term is retained in the Russian word for the animal , кашалот ( kashalot ) , as well as in many other languages . 
