lenition (n.)

A term used in PHONOLOGY to refer to a weakening in the overall strength of a sound, whether DIACHRONICALLY or SYNCHRONICALLY; opposed to fortition. Typically, lenition involves the change from a STOP to a FRICATIVE, a fricative to an APPROXIMANT, a voiceless sound to a VOICED sound, or a sound being reduced (lenite) to zero. For example, the initial MUTATION in Celtic languages shows lenition in such cases as Welsh pen ‘head’ becoming ben ‘(his) head’.