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rhotacism

noun

Historical Linguistics. a change of a speech sound, especially (s), to (r), as in the change from Old Latin lases to Latin lares.
excessive use of the sound (r), its misarticulation, or the substitution of another sound for it.

noun phonetics

excessive use or idiosyncratic pronunciation of r

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 (cf. the “burr”), especially the conversion of another sound (usually -s-) to -r-; cf. Aeolian Greek, which at the end of words changed -s- into -r- (hippor for hippos, etc.). Related: Rhotacize.