'first-string' definitions:

Definition of 'first-string'

(from WordNet)
adjective
Of members of a team; not substitutes
adjective
Being a regular member of a team; "first-string players"

Definition of 'first-string'

From: GCIDE
  • first-string \first-string\ adj. First to play in a game; not reserved as a substitute; -- of members of a team. Also used in non-sports contexts to mean first-rate. [WordNet 1.5 +PJC]