Lenition

Definition
Lenition''' is a process of weakening. The diachronic development in (i) can be analyzed as a case of lenition (Hooper (1976), Katamba (1989)):

(i)      Latin	 Italian  Spanish  French vita	 vita	 vida	   vie	  'life' t -&gt;  t   -&gt;   d   -&gt;    0

Lenition can be explained by referring to the sonority hierarchy : the progression down the sonority hierarchy is from a voiceless stop to a voiced stop before deletion takes place. Lenition can also occur in one language.

Link

 * Utrecht Lexicon of Linguistics