raising

 In phonology and phonetics, raising is a sound change in which a vowel or consonant becomes higher or raised, meaning that the tongue becomes more elevated or positioned closer to the roof of the mouth than before.

dissimilation

 In phonology, particularly within historical linguistics, dissimilation is a phenomenon whereby similar consonants or vowels in a word become less similar. In English, dissimilation is particularly common with liquid consonants such as /r/ and /l/ when they occur in a sequence. 

For example, Latin peregrinus > Old French pelegrin (and the Italian pellegrino and Sicilian piḍḍigrinu) which gave rise to the English pilgrim.