Definitions of mask:

• noun:   activity that tries to conceal something

  Example: "No mask could conceal his ignorance"

• noun:   a covering to disguise or conceal the face
• noun:   a protective covering worn over the face
• noun:   a party of guests wearing costumes and masks
• verb:   put a mask on or cover with a mask

  Example: "Mask the children for Halloween"

• verb:   shield from light
• verb:   cover with a sauce

  Example: "Mask the meat"

• verb:   hide under a false appearance

  Example: "He masked his disappointment"

• name:  A surname (rare: 1 in 50000 families; popularity rank in the U.S.: #7262)