rhotacism (n.)

1830, from Modern Latin rhotacismus, from Greek rhotakizein, from rho "the letter -r-," from Hebrew or Phoenician roth. Excessive or peculiar use of the -r- sound (the "burr"), especially the conversion of another sound (usually -s-) to -r-; as in Aeolian Greek, which at the end of words changed -s- into -r- (hippor for hippos, etc.). Related: Rhotacize.