Rhotacism \Rho"ta*cism\, n. [Gr. "rwtaki`zein to use the letter
r ([rho]) overmuch: cf. F. rhotacisme.]
An oversounding, or a misuse, of the letter r; specifically
(Phylol.), the tendency, exhibited in the Indo-European
languages, to change s to r, as wese to were.
[1913 Webster]