BETACISM

Noun

betacism (usually uncountable, plural betacisms)

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

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

Source: Wiktionary

Be"ta*cism, Be`ta*cis"mus, n.

Definition: Excessive or extended use of the b sound in speech, due to conversion of other sounds into it, as through inability to distinguish them from b, or because of difficulty in pronouncing them.

Source: Webster’s Unabridged Dictionary 1913 Edition