Contact assimilation vs. distant assimilation

In case of contact assimilation (also called immediate assimilation) the sound undergoing assimilation and the one causing it are immediately adjacent: Old English efn 'even' > West-Saxon emn. In case of distant assimilation the two sounds are not adjacent: Proto-Indo-European *penkʷe > Latin kʷinkʷe (spelled quinque). When distant assimilation applies over an entire word it is called harmony (e.g. vowel harmony, nasal harmony).

Other languages
German Kontaktassimilation vs. Distanzassimilation