also: ワッチキャップ
noun
watch cap; beanie
A close-fitting knitted cap, often worn in cold weather or as part of a casual outfit. The term is a direct loan from English.
冬はウォッチキャップをかぶって耳を温める。
In winter, I wear a watch cap to keep my ears warm.
彼は黒いウォッチキャップを深くかぶっていた。
He was wearing a black watch cap pulled down low.
ニット帽 is a broader term for any knitted hat, while ウォッチキャップ specifically refers to the close-fitting, often cuffless style associated with sailors or casual wear.
Borrowed from English 'watch cap', referring to the knitted cap traditionally worn by sailors on watch duty.