narwhal

noun

1. a medium-sized Arctic toothed whale, the male of which has a long, straight, spiral tusk (an elongated tooth) projecting from the upper jaw

   countable

   • "The narwhal is often called the unicorn of the sea."A2
   • "Narwhals use their long tusks to sense changes in water temperature and salinity."B1
   • "Climate change is rapidly diminishing the sea-ice habitat on which narwhals depend for survival."C1

2. the tusk of a narwhal whale, sometimes historically traded as a unicorn horn

   countablehistorical

   • "In medieval times, a narwhal tusk was often sold as a unicorn horn."B2