Source : Webster's Revised Unabridged Dictionary (1913)

Nebulous \Neb"u*lous\, a. [L. nebulosus: cf. F. n['e]buleux. See
   {Nebula}.]
   1. Cloudy; hazy; misty.

   2. (Astron.) Of, pertaining to, or having the appearance of,
      a nebula; nebular; cloudlike. -- {Neb"u*lous*ly}, adv. --
      {Neb"u*lous*ness}, n.

Source : WordNet®

nebulously
     adv : in a nebulous and indefinite manner