is a construction comprised of the conjunctive form of だ, で, the particle しか, and the い-Adjective, ない. Like all other しか based structures, it is used to indicate that the target word is ‘no more than (A)’, or ‘merely (A)’. The primary difference with でしかない
compared to other similar grammar patterns is that it will only appear directly after nouns.
That is nothing but an excuse.
My senpai says that he is saying this out of love, but it’s nothing more than abusive language.
To my son, it is something precious, but to me it is nothing but garbage.
can be used with either a positive or negative nuance, it tends to be seen more frequently with a slightly negative nuance in relation to (A), indicating that it has no value or significant meaning beyond (A).