Learn Farsi: عهد راهب، حرف نزدن در صومعه است. - The monk's vow is not speaking in the monastery.

The infinitive for "to speak" is حرف زدن. To make it negative, you add the negative prefix نـ (na-) directly to the verbal part of the infinitive, becoming نزدن. Since it is a compound verb, the non-verbal part (حرف) stays separate: حرف نزدن. Here, it functions perfectly as a noun phrase meaning "not speaking."

Could we use a subjunctive clause instead of the negative infinitive here?

Yes! While using the negative infinitive حرف نزدن is a very concise way to express this, you could also use a clause with که (that) and the negative subjunctive. It would look like: عهد راهب این است که در صومعه حرف نزند (The monk's vow is this, that he not speak in the monastery). At the B2 level, you will often see authors swap between these two structures depending on how formal they want to be.

What is the word for "monastery" and how do you pronounce the ع in the middle of it?

The word is صومعه (soume'e). Because it is an Arabic loanword, it contains the letter ع (ain). In standard modern Farsi, this letter usually just represents a glottal stop (a tiny catch in the throat, like the middle of "uh-oh") or a smooth transition between the vowels, rather than a distinct consonant sound.

Why is there a comma after راهب?

In written Farsi, commas are often used more flexibly than in English to mark a natural pause in speech or to visually chunk parts of a sentence. Here, it simply shows where the subject phrase (عهد راهب, the monk's vow) ends, preventing the reader from accidentally blending the subject into the predicate.