Im*plo"sion (?), n. [Formed by substitution of pref. im- in for pref. ex- in explosion.]
A bursting inwards, as of a vessel from which the air has been exhausted; -- contrasted with explosion.
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, §§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.
© Webster 1913.
[Editor's Note (Gz), 12/23/2002: corrected apparent scan error (although it's fun to think that "burstion" is a real word)]