According to Tang Rhymes (Tang Yun) and Collected Rhymes (Jiyun), the pronunciation is shi. Pronounced shi (falling tone). The Jade Chapter (Yupen) defines it as a face covering. Additionally, in Extensive Rhymes (Guangyun) and Collected Rhymes (Jiyun), it is also given the pronunciation yi. Pronounced yi (falling tone). The meaning is the same.