From Longman Dictionary of Contemporary Englishskull capˈskull cap noun [countable] DCCa small round close-fitting hat for the top of the head, worn sometimes by Christian priests or Jewish men
Examples from the Corpus
skull cap• The pale woman, bosom exposed, is entwined with a dark man wearing a sullen expression and a skull cap.• It is a Walkman-sized device wired to a skull cap that monitors brain waves.• I recognized the neat plastic skull cap.• His close-cropped hair was hidden under a black velvet skull cap. 