いち

In a sentence

• 彼は一番の選手です。

  He is the best player.

  Here, "いち" is part of "一番 (いちばん)", meaning "the best" or "number one", indicating ranking.

• 机の上に一冊の本があります。

  There is a book on the desk.

  Here, "いち" is part of "一冊 (いっさつ)", which counts one book, indicating quantity.

• この辺りには一度も行ったことがありません。

  I have never been to this area even once.

  Here, "いち" is part of "一度 (いちど)", indicating a single occurrence or attempt in time.