deleznarse

A reflexive verb meaning to crumble, disintegrate, or slip away — used literally for materials that fall apart (una roca que se deleznaba) and figuratively for arguments or positions that don't hold up (un argumento deleznable, from the same root, is far more common than the verb itself). It leans literary/formal register.

• La piedra se deleznaba entre los dedos. — The stone crumbled between my fingers.
• Su excusa se deleznó ante la primera pregunta. — His excuse fell apart at the first question.
• El terreno se deleznaba con cada lluvia. — The ground eroded with every rain.

Learners rarely meet the verb itself since the adjective deleznable ("flimsy," "contemptible") is far more common in everyday Spanish — don't be surprised if this verb sounds unfamiliar even at an advanced level.