Definition of "understudy" []

• To study or know (a role) so as to be able to replace the regular performer when required. (verb-transitive)
• To act as an understudy to. (verb-transitive)
• To be engaged in studying a role so as to be able to replace the regular performer when required. (verb-intransitive)
• A performer who understudies. (noun)
• A person trained to do the work of another. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "With Almunia rated doubtful for Sunday's trip to Stamford Bridge, his former understudy is on stand-by."
• "If he dies or explodes in scandal, Hannity or some other understudy is waiting in the wings."
• "Bridge has been the long-term understudy to Ashley Cole for England's left-back position, and with the Chelsea defender ruled out for three months after breaking his ankle at Everton on Wednesday would seem to be first in line to take his place in the team."