betacism

/B EH1 T AH0 S IH0 Z AH0 M/
noun
  1. 1

    (phonology) A sound change in which [b] (the voiced bilabial plosive) shifts to [v] (the voiced labiodental fricative).

  2. 2

    A speech disorder involving excessive use of the [b] sound, or conversion of other sounds into it.