The term 'white as a sheet' is often used to describe someone who is very PALE or frightened. The crossword solutions for this term are PALE (4 letters), ASHEN (5 letters), AGHAST (6 letters), and PASTYFACED (10 letters). PALE is an adjective meaning having a very low level of color, while ASHEN means having a grayish-white color. AGHAST is an adjective meaning filled with shock or horror, and PASTYFACED is an adjective meaning having a PALE complexion.