I seem to keep running into words like these. The definitions of them are pretty vague but I think I get the idea.
sibilant - a consonant characterized by a hissing sound (like s or sh)
fricative, spirant - A consonant, such as f or s in English, produced by the forcing of breath through a constricted passage.
rhotacism, rotacism - An oversounding, or a misuse, of the letter r
lambdacism - speech defect involving excessive use or unusual pronunciation of the phoneme `l'