blue whale

noun

1. a migratory baleen whale, Balaenoptera musculus, mostly of oceans and seas in the Southern Hemisphere, growing to a length of 100 feet (30.5 meters) and having a furrowed, slate-blue skin mottled with lighter spots, in some seas acquiring a yellowish coating of diatoms on the underside: the largest mammal ever known, it is now endangered.

noun

1. the largest mammal: a widely distributed bluish-grey whalebone whale, Sibbaldus (or Balaenoptera) musculus, closely related and similar to the rorquals: family BalaenopteridaeAlso called: sulphur-bottom