godan verb (-ru), intransitive verb
narrow; become thin; taper
Intransitive verb describing something becoming narrower or thinner, often used for eyes narrowing into a slit or a path tapering. Less common than the transitive counterpart 細める.
彼は眩しそうに目が細まった。
His eyes narrowed as if the light were too bright.
道が山の上
The path narrows as it goes up the mountain.