understudy
1. un.der.study \-.st*d-e-, .*n-d*r-'\ vi : to study another actor's part in order to be his substitute in an emerg ency to prepare (as a part) as understudy; also : to prepare as understudy to (as an actor) 2. un.der.study \'*n-d*r-.st*d-e-\ n : one who stands prepared to act another's part or take over another's dut ies