ichidan verb, intransitive verb
become gaunt; become hollow-cheeked; get scrawny
Describes a person's face or body becoming thin and hollow-looking, often due to age, illness, or fatigue. Intransitive verb.
病気で顔がこけてしまった。
His face became gaunt from illness.
年を取ると、ほおがこける
As you get older, your cheeks may become hollow.