In linguistics, lenition is a sound change that alters consonants, making them "weaker" in some way. The word lenition means 'softening' or 'weakening' (from Latin lēnis 'weak'). Lenition can happen both synchronically (within a language at a particular point in time) and diachronically (as a language changes over time). Lenition can involve such changes as voicing a voiceless consonant, causing a consonant to relax occlusion, to lose its place of articulation (a phenomenon called debuccalization, which turns a consonant into a glottal consonant like [h] or [ʔ]), or even causing a consonant to disappear entirely.
An example of synchronic lenition is found in most varieties of American English, in the form of tapping: the /t/ of a word like wait [weɪt] is pronounced as the more sonorous [ɾ] in the related form waiting [ˈweɪɾɪŋ]. Some varieties of Spanish show debuccalization of /s/ to [h] at the end of a syllable, so that a word like estamos "we are" is pronounced [ehˈtamoh]. An example of diachronic lenition can be found in the Romance languages, where the /t/ of Latin patrem ("father", accusative) has become /d/ in Italian (an irregular change; compare saeta "silk" > seta) and Spanish padre (the latter weakened synchronically /d/ → [ð̞]), while in Catalan pare, French père and Portuguese pai historical /t/ has disappeared completely.