Noun

• S: (n) understudy, standby (an actor able to replace a regular performer when required)
• direct hypernym / inherited hypernym / sister term
• S: (n) actor, histrion, player, thespian, role player (a theatrical performer)
• derivationally related form

Verb

• S: (v) understudy, alternate (be an understudy or alternate for a role)
• direct hypernym / inherited hypernym / sister term
• S: (v) memorize, memorise, con, learn (commit to memory; learn by heart) "Have you memorized your lines for the play yet?"
• derivationally related form
• sentence frame