Simile

A figure of speech that makes a comparison between two unlike things and uses the words "like," "as," "than," or "resembles."

Example From Text

...the Narwhal crossed Queen Charlotte Sound and rolled and pitched and bucked like a thing possessed.

Explanation

London compares the boat, the Narwhal, with a "thing possessed," which means something that's wild or insane. The comparison helps the reader understand the violence of the ship's pitching and rolling in the rough water.