be thin on top

US /bi θɪn ɑn tɑp/
UK /bi θɪn ɑn tɑp/
"be thin on top" picture
1.

to have very little hair on the top of one's head; to be going bald

:
He started to be thin on top in his late twenties.
My grandfather used to joke that he was just thin on top, not bald.