Source : Webster's Revised Unabridged Dictionary (1913)

Overtime \O"ver*time`\, n.
   Time beyond, or in excess of, a limit; esp., extra working
   time.

Source : WordNet®

overtime
     n 1: work done in addition to regular working hours
     2: playing time beyond regulation, to break a tie [syn: {extra
        time}] [ant: {regulation time}]

overtime
     adv : beyond the regular time; "she often has to work overtime"