This is the 8432nd most frequent Catalan word.
dimitís
"Dimitis" means "you resigned" or "he/she resigned" in English (second or third person singular, past tense of "dimitir").
In this example, 'dimitís' is used in the subjunctive form to describe a hypothetical situation.
Si dimitís, n'hauríem de buscar un substitut.
If he resigned, we would need to find a replacement.
The word 'dimiteixi' is used in the present subjunctive to express a desire or expectation about the future.
Espero que no dimiteixi abans que finalitzi el projecte.
I hope he doesn't resign before the project is finished.
Here, 'dimitir' is used in the past tense indicated by 'va dimitir', meaning the act of resigning completed in the past.