only, merely
Indicates that something is limited to what is stated, conveying a sense of confinement or restriction.
Examples
彼の意見は一人の考えでしかない。
His opinion is merely one person's view.
私の考えはこれでしかない。
My thought is only this.
それは誘惑でしかない。
That is nothing but temptation.
Quick check
彼の意見は一人の考え___。