低顶帽
a hat that is not rounded on top and has little height
He was wearing a flat cap and a black jacket.
He doffed his flat cap and smiled pleasantly.
We were joined by a short man with a flat cap.
He was wearing a flat cap made of tweed.
He rode towards them on his bicycle, raising his flat hat in greeting.
She had a brown, cord flat hat on her head.
She wore an eye-catching pink flat hat.
See also: flat adjective (NOT HIGH)