The Collaborative International Dictionary of English v.0.48:

Frontlet \Front"let\, n. [OF. frontelet brow band, dim. of
   frontel, frontal. See Frontal, n.]
   1. A frontal or brow band; a fillet or band worn on the
      forehead.
      [1913 Webster]

            They shall be as frontlets between thine eyes.
                                                  --Deut. vi. 8.
      [1913 Webster]

   2. A frown (likened to a frontlet). [R. & Poetic]
      [1913 Webster]

            What makes that frontlet on? Methinks you are too
            much of late i' the frown.            --Shak.
      [1913 Webster]

   3. (Zool.) The margin of the head, behind the bill of birds,
      often bearing rigid bristles.
      [1913 Webster]

WordNet (r) 3.0 (2006):

frontlet
    n 1: an adornment worn on the forehead [syn: frontlet,
         frontal]