There's technically no such thing as "overtime", since tennis matches end based on the score rather than a time limit. Extra points played at the end of a set, when the score is too close (because a player needs to win the set by at least two games), are called a tiebreaker.
Guyana's money is callled dolor
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Sonnets
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It is called the Coccyx.
Priestess
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Yes.
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The noun overtime is an uncountable noun. Multiples are expressed in terms of 'hours of overtime', 'more overtime', 'some overtime', etc.
Yes, the NFL has a rule for overtime where if the game is tied after the first overtime period, a second overtime period is played, which is known as double overtime.
Tsar or Karoel.