A yashmak is a face veil — a piece of cloth some Muslim women wear over the lower half of the face in public, usually leaving the eyes showing. The word is specifically Turkish in origin and is tied to Ottoman Turkey, so it carries an old, historical feeling in English. You will find it in older travel writing, novels, and books about the Ottoman Empire far more often than in today's news. When modern English writes about face coverings it normally uses niqab or burqa, which name different garments worn in different places; a careful writer does not use these words as if they were the same thing. So treat yashmak as a slightly literary or historical word: correct, but marked. It is a countable noun — a yashmak, two yashmaks — and English also says "wearing a yashmak" rather than "in a yashmak", though both occur.

（土耳其式）面紗