cast·​mate | \ ˈkast-ˌmāt also ˈkäst-\
plural castmates

Definition of castmate

: a fellow member of a cast of actors I look at some of my castmates and see all the great acting they're doing …— Kristin Bauer van Straten, quoted in Tampa Bay Times, 14 June 2013

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First Known Use of castmate

1931, in the meaning defined above

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The first known use of castmate was in 1931

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