Learn Turkish: Kurşun geçirmez yelekleri ormanda test ettik. - We tested the bulletproof vests in the forest.

The root verb is geçirmek, which means "to let pass" or "to transmit". By adding the negative aorist participle suffix -mez, it becomes an adjective meaning "that which does not let pass". Combined with kurşun (bullet), it literally means "bullet non-passing"—or "bulletproof".

Why is kurşun singular here when a vest prevents multiple bullets?

In Turkish, when a noun is paired with a participle to form a compound adjective (like kurşun geçirmez), the noun usually stays singular because it represents a general category, not specific items. English does the exact same thing: we say "bulletproof," not "bulletsproof."

Why is the suffix -i added to yelekler to make yelekleri?

The suffix -i is the definite accusative case marker. We use it because the vests are the specific direct object of the verb test ettik. We aren't testing just any vests in general; we are testing the specific bulletproof vests.

Why is test ettik written as two words instead of being combined like some other etmek verbs?