The Nanukapik is a rank meaning 'greatest bear' in Inuit language. The Nanukapik is the leader of the polar bears. Gwilanna first uses it in a contemptful way when she refers to their 'Nanukapik' being unable to stop the ice from melting due to global warming. We later find out the meaning when David Rain asks Dr. Bergstrom about the word.
When David was killed via being impaled by an ice shard (in reality, a frozen piece of Gawain's Fire Tear), his soul merged with that of Ingavar, and he returns in The Fire Eternal as a Nanukapik in the form of Ingavar.