決きめ手てに欠かける

expression, ichidan verb

lack a decisive factor; lack a trump card; lack conclusive evidence

Used when a situation, argument, or investigation is missing the one decisive element that would settle it. Often appears in contexts like debates, games, or criminal cases.

• 彼かれの主しゅ張ちょうはもっともだが、決きめ手てに欠かける。

  His argument is reasonable, but it lacks a decisive factor.

• 捜そう査さは進すすんでいるが、まだ決きめ手てに欠かける。

  The investigation is progressing, but it still lacks conclusive evidence.