guest star

Short definition from Wiktionary

Noun

1. 1
   A guest on a music or other recording.
2. 2
   An actor on a television program who stars in one, or a few, episodes.
3. 3
   A nova or supernova recorded in Chinese astronomy which appeared where no star was known before.
4. 4
   Alternative form of guest star.

Verb

1. 1
   Of an actor: to star as a guest.
2. 2
   Of a player: to play as a guest of another team.
3. 3
   Alternative form of guest star.