expression, noun which may take the genitive case particle 'no'
Emphasizes that there is exactly one, often with a nuance of scarcity or uniqueness. Used as a prenominal modifier with の.
See also: たった
冷蔵庫にたった一つの卵しかない。
There is only one egg in the fridge.
彼はたった一つのチャンスを逃した。
He missed his only chance.