From The Collaborative International Dictionary of English v.0.48:
Mask \Mask\, v. t. [imp. & p. p. Masked; p. pr. & vb. n. Masking.] 1. To cover, as the face, by way of concealment or defense against injury; to conceal with a mask or visor. [1913 Webster]
They must all be masked and vizarded. --Shak. [1913 Webster]
2. To disguise; to cover; to hide. [1913 Webster]
Masking the business from the common eye. --Shak. [1913 Webster]
3. (Mil.) (a) To conceal; also, to intervene in the line of. (b) To cover or keep in check; as, to mask a body of troops or a fortress by a superior force, while some hostile evolution is being carried out. [1913 Webster]