Assimilation

Assimilation is a sound change in which some phonemes (typically consonants or vowels) change to become more similar to other nearby sounds. A common type of phonological process across languages, assimilation can occur either within a word or between words.

Sources:

Sihler, Andrew L. (2000). Language History: An Introduction.

Meyer, Paul Georg (2005). Synchronic English Linguistics: An Introduction.