steam up

Verb

steam up (third-person singular simple present steams up, present participle steaming up, simple past and past participle steamed up)

1. To become steamy.
2. To become coated with condensation.
   • The bathroom mirror steamed up when he opened the shower door.
   • The large plateglass window, from which I had an excellent view of the countryside the following day, was prevented from steaming up by a de-misting device.1953 July, Allen Rowley, “First Impressions of American Railways”, in Railway Magazine, page 493

   Synonyms:

   fog up

3. (transitive) To bring (a steam boiler) up to working steam pressure: to build up a head of steam inside (a boiler).
   • It takes about an hour to steam up the locomotive.
4. (intransitive) to build up a head of steam.
   • Engine 99 had been steaming up since 21:00.
   • "The master of the Nan-Shan [...] desired Mr. Rout to have steam up to-morrow afternoon at one o'clock sharp."1919, Joseph Conrad, Typhoon, page 8
5. (transitive) To cook by steaming.
   • I'll steam up a bunch of dumplings.