To substitute for; to replace; (theater) to serve as an understudy.
To make one of a party in a bet or other speculation.
To take a side in a dispute.
A substitute; a replacement.
To act as an understudy (to someone).
To study or know a role to such an extent as to be able to replace the normal performer when required.
To act in a similar manner to some known person.
A performer who understudies; a standby.