under-study

verb (used with object), un·der·stud·ied, un·der·stud·y·ing.

1. to learn (a role) in order to replace the regular actor or actress when necessary.
2. to act as understudy to (an actor or actress): to understudy the lead.

verb (used without object), un·der·stud·ied, un·der·stud·y·ing.

3. to act or work as an understudy.

noun, plural un·der·stud·ies.

4. a performer who learns the role of another in order to serve as a replacement if necessary.

verb -studies, -studying or -studied

1. (tr) to study (a role or part) so as to be able to replace the usual actor or actress if necessary
2. to act as understudy to (an actor or actress)

noun plural -studies

3. an actor or actress who studies a part so as to be able to replace the usual actor or actress if necessary
4. anyone who is trained to take the place of another in case of need

v.also under-study, 1852, in the theatrical sense, from under + study (v.). The noun is attested from 1848, translating Italian supplimento.