Source : Webster's Revised Unabridged Dictionary (1913)

Stilly \Still"y\, a.
   Still; quiet; calm.

         The stilly hour when storms are gone.    --Moore.

Stilly \Stil"ly\, adv.
   In a still manner; quietly; silently; softly. --Dr. H. More.

         The hum of either army stilly sounds.    --Shak.

Source : WordNet®

stilly
     adj : (poetic) still or calm; "in the stilly night"