The Collaborative International Dictionary of English v.0.48:

effusive \ef*fu"sive\, a.
   1. Pouring out; pouring forth freely. [archaic] "Washed with
      the effusive wave." --Pope.
      [1913 Webster]

   2. (Geol.) formed by an outpouring of molten lava, or
      pertaining to rocks so formed.
      [PJC]

   3. overly demonstrative; expressing emotion in an
      unrestrained manner; exhibiting unrestrained enthusiasm;
      -- of people and human actions; as, effusive thanks; an
      effusive letter of recommendation. Contrasted with
      reserved. [WordNet sense 1+2]

   Syn: gushing, gushy, burbling, burbly. [PJC]

   Effusive rocks (Geol.), volcanic rocks formed by a
      nonexplosive outpouring of lava in molten or plastic form;
      in distinction from so-called intrusive, or plutonic,
      rocks. -- Ef*fu"sive*ly, adv. -- Ef*fu"sive*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

effusively
    adv 1: in an effusive manner; "the critics praised her
           effusively"