Source : Webster's Revised Unabridged Dictionary (1913)

Impressive \Im*press"ive\, a. [Cf. F. impressif.]
   1. Making, or tending to make, an impression; having power to
      impress; adapted to excite attention and feeling, to touch
      the sensibilities, or affect the conscience; as, an
      impressive discourse; an impressive scene.

   2. Capable of being impressed. [Obs.] --Drayton. -
      {Im*press"ive*ly}, adv. -- {Im*press"ive*ness}, n.

Source : WordNet®

impressiveness
     n : splendid or imposing in size or appearance; "the grandness
         of the architecture" [syn: {grandness}, {magnificence}]