The Collaborative International Dictionary of English v.0.48:

Curtain \Cur"tain\, v. t. [imp. & p. p. Curtained
   (k[^u]r"t[i^]nd; 48); p. pr. & vb. n. Curtaining.]
   To inclose as with curtains; to furnish with curtains.
   [1913 Webster]

         So when the sun in bed
         Curtained with cloudy red.               --Milton.
   [1913 Webster]