lenition

[li-nish-uh n] /lɪˈnɪʃ ən/
noun
1.
Phonetics. a phonological process that weakens consonant articulation at the ends of syllables or between vowels, causing the consonant to become voiced, spirantized, or deleted.
2.
Linguistics. a type of Celtic mutation that derives historically from phonological lenition.
Origin
1535-45 for obsolete sense “mitigation, assuaging”; 1910-15 for current senses; < Latin lēnīt(us) (past participle of lēnīre to soften; see lenis, -ite2) + -ion