can

"Can" is one of the most commonly used modal verbs in English. It can be used to express ability or opportunity, to request or offer permission, and to show possibility or impossibility.

「できる」という意味だけではなく他の意味でも使えます。
・general ability
・ability during a specific event
・permission
・request
・possibility, impossibility

イディオムでは・・・

「〜せざるを得ない」
I cannot laughing whenever I think of his joke.
I cannot but laugh whenever I think of his joke.

「いくら〜してもし足りない」
I cannot praise this dictionary enough.
I cannot praise this dictionary too much.


↓be able to, may, could, も併せて説明されてます。
englishpage.com「Can」
https://www.englishpage.com/modals/can.html