1. A front or boundary, especially one between military, political, or ideological positions.

2. Basketball See frontcourt.

3. Football The linemen of a team.

4. Sports The players who play farthest forward, as in volleyball.

1. Located or used at a military front.

2. Of or relating to the most advanced or important position or activity in a field or undertaking: "elicited candid revelations from many of the front-line executives ... and doggedly followed the money trail down all its byways" (Steve Fraser).

3. Sports

4. Performing the most basic tasks or interacting directly with customers, patients, or clients: a frontline caregiver; frontline caseworkers.