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]
From The Collaborative International Dictionary of English v.0.48:
Masked \Masked\, a. 1. Wearing a mask or masks; characterized by masks; concealed; hidden. [1913 Webster]
2. (Bot.) Same as Personate. [1913 Webster]
3. (Zool.) Having the anterior part of the head differing decidedly in color from the rest of the plumage; -- said of birds. [1913 Webster]
Masked ball, a ball in which the dancers wear masks.
Masked battery (Mil.), a battery so placed as not to be seen by an enemy until it opens fire. --H. L. Scott.
Masked crab (Zool.), a European crab (Corystes cassivelaunus) with markings on the carapace somewhat resembling a human face.
Masked pig (Zool.), a Japanese domestic hog (Sus pliciceps). Its face is deeply furrowed. [1913 Webster]