Learn Turkish: Yeni kırışmaz pantolonumu yırtılana kadar giydim. - I wore my new wrinkle-free trousers until they tore.

It comes from the verb kırışmak (to wrinkle). In this lesson, we add the negative aorist suffix -maz (or -mez) to a verb to create an adjective that describes something that generally never does that action. So, kırışmaz pantolon literally means "trousers that do not wrinkle."

How is "until they tore" formed in yırtılana kadar?

To say "until [an action] happens," Turkish uses the verb root + the suffix -(y)ana or -(y)ene, followed by kadar. Here, the verb root is yırtıl-, so we add -ana to connect it to kadar. Notice that even though the English translation is in the past tense ("until they tore"), the Turkish structure itself doesn't have a past tense marker; the time is understood from the main verb, giydim (I wore).

Why is the verb yırtılmak used here instead of yırtmak?

Yırtmak is an active verb meaning "to tear [something]," like when you tear a piece of paper. Yırtılmak adds the passive suffix -ıl, meaning "to be torn." We use the passive form here because the trousers aren't tearing anything else; they are the things getting torn.

Why is there an extra -u at the end of pantolonumu?