dissimilate

Concise Oxford English Dictionary © 2008 Oxford University Press:
dissimilate /dɪˈsɪmɪleɪt/

▶verb Linguistics change (a sound in a word) to another when the word originally had identical sounds near each other (e.g. in taper, which derives from papyrus, the p is dissimilated to t).

– derivatives
dissimilation noun,
dissimilatory adjective.

– origin C19: from dis- + L. similis ‘like, similar’, on the pattern of assimilate.