expression, i-adjective
is nothing but; is only; is no more than
Follows a noun or na-adjective stem to emphasize that something is merely that and nothing more, often with a dismissive or minimizing tone.
それはただの噂でしかない。
That's nothing but a rumor.
彼の言い分は言い訳でしかない。
His claim is nothing more than an excuse.