This is the 8972nd most frequent Japanese word.
決ま
"決ま" (きま) is a stem of the verb "決まる," meaning "to be decided" or "to be determined."
In this example, '決まった' (kimatta) is used to express that the meeting time has finally been settled or fixed.
待ち合わせの時間がやっと決まった。
The meeting time has finally been decided.
In this sentence, '決まります' (kimarimasu) is used to indicate a decision or determination being made about the outcome of the match.
その試合の勝敗が今日決まります。
The outcome of that match will be decided today.
Here, '決まっている' (kimatte iru) conveys that the hairstyle consistently looks well-arranged or stylish.