"understudy" in the noun sense
1. understudy, standby
an actor able to replace a regular performer when required
"understudy" in the verb sense
1. understudy, alternate
be an understudy or alternate for a role
Source: WordNet® (An amazing lexical database of English)
Princeton University "About WordNet®."
WordNet®. Princeton University. 2010.
View WordNet® License