second-string
adjectiveUK /ˌsekənd ˈstrɪŋ/
US /ˌsekənd ˈstrɪŋ/
A second-string player is a backup who plays when the main player cannot.
The coach put in a second-string player after the starter got hurt.
OTHER MEANINGS
2. Not the best or most important of its kind; of lesser quality.
They sent a second-string team to the tournament.
3. A player on a backup or reserve group of a sports team.
He spent two seasons as a second-string before earning a starting spot.
4. A person or thing used as a fallback option.
The company kept a second-string supplier in case of delays.