Webster's Revised Unabridged Dictionary · 1913

defrost

defrost , transitive verb

To remove the frost or ice from; as, to defrost the car window; to defrost a refrigerator.

defrost , intransitive verb

1.
To become free of frost or ice; as, it took four hours for the refrigerator to defrost.
2.
To thaw; -- used especially of items removed from a freezer, such as frozen foods.