The Collaborative International Dictionary of English v.0.48:
Overtime \O"ver*time`\, n.
1. Time beyond, or in excess of, a limit; esp., extra working
time.
[1913 Webster]
2. (Sports) An extra period of time provided to play a game,
beyond the end of the normal period allowed for the game,
for the purpose of resolving a tie score; as, the team won
in overtime.
[PJC]
sudden death overtime an overtime[2] in which the first
team to score wins the game; -- contrasted with normal
overtime[2], which is a fixed period of time during which
either team may score as often as they can.
[PJC]