This is the 3687th most frequent Japanese word.
いち
"いち" means "one" in English.
Here, "いち" is part of "一番 (いちばん)", meaning "the best" or "number one", indicating ranking.
彼は一番の選手です。
He is the best player.
Here, "いち" is part of "一冊 (いっさつ)", which counts one book, indicating quantity.
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 "一度 (いちど)", indicating a single occurrence or attempt in time.