Learn Arabic (Modern Standard): اشتريت مطحنة من السوق لأنني أريد أن أطحن القهوة. - I bought a grinder from the market because I want to grind the coffee.

مطحنة follows the مِفْعَلَة (mif'alah) pattern, which is one of the standard ways to create a noun of instrument (a word for a tool). It comes from the root for grinding, so it literally means an instrument used to grind.

I see أطحن later in the sentence. Are these two words directly related?

Yes! They share the exact same three-letter root: ط - ح - ن (t-h-n), which has to do with grinding or crushing. أطحن is the present tense verb meaning I grind, while مطحنة uses the tool pattern to mean grinder. This shows how Arabic builds related vocabulary from a single root.

Why does the verb أطحن end with an a vowel instead of the usual u vowel?

Because it comes right after the particle أن (to). When a present tense verb follows أن, it goes into the subjunctive state. For regular verbs like this one, that means changing the final u vowel (Damma) to an a vowel (Fatha). So it is pronounced an aṭḥana instead of an aṭḥanu.

How is the word لأنني (because I) put together?

It is made of three pieces glued together: لِـ (li) meaning for, أنّ (anna) meaning that, and the attached pronoun ـني (ni) meaning I or me. Combined as لأنني, they translate smoothly into English as because I.