Progressive assimilation vs. regressive assimilation

Regressive assimilation is an assimilation in which the sound that undergoes the change (the target) comes earlier in the word than the trigger of assimilation, in other words the change operates backwards: Latin septem 'seven' > Italian sette. In case of progressive assimilation the trigger comes before the target so that the assimilation operates forwards: Proto-Germantic *wulno 'wool' > Old English wull. In rare cases of reciprocal assimilation there is a mutual influence between the two sounds.

Synonyms
Regressive assimilation is also called anticipatory assimilation or right-to-left assimilation.

Progressive assimilation is also known as perseveratory assimilation or left-to-right assimilation.

Other languages
German progressive Assimilation vs. regressive Assimilation