まるっきり is a strong adverb that means 'completely' or 'totally'. When used with a positive statement, it emphasizes that something is exactly as described, e.g., まるっきり同じ (exactly the same). However, it is far more common in negative sentences, where it means '(not) at all', as in まるっきり分からない (I don't understand at all). In this usage, it pairs with a negative verb or adjective at the end of the clause.

This word is fairly emphatic and often carries a sense of surprise or frustration. It is used in both spoken and written Japanese, but in casual speech, it is not unusual to drop the negative ending and imply it, like まるっきりダメ (totally useless). However, for learners, it's safer to always use the full negative form to avoid ambiguity.

Note that まるっきり is not the same as まったく (totally), which is more neutral. まるっきり often implies that the speaker finds the situation extreme or noteworthy.