Source : Webster's Revised Unabridged Dictionary (1913)

Implosion \Im*plo"sion\, n. [Formed by substitution of pref. im-
   in for pref. ex- in explosion.]
   1. A burstion inwards, as of a vessel from which the air has
      been exhausted; -- contrasted with explosion.

   2. (Phon.) A sudden compression of the air in the mouth,
      simultaneously with and affecting the sound made by the
      closure of the organs in uttering p, t, or k, at the end
      of a syllable (see Guide to Pronunciation,
      [sect][sect]159, 189); also, a similar compression made by
      an upward thrust of the larynx without any accompanying
      explosive action, as in the peculiar sound of b, d, and g,
      heard in Southern Germany. --H. Sweet.

Source : WordNet®

implosion
     n 1: a sudden inward collapse; "the implosion of a light bulb"
     2: the initial occluded phase of a stop consonant