https://en.m.wikipedia.org/wiki/Stutter_(disambiguation) reads: "A stutter, or stuttering is a speech disorder characterized by the spasmodic repetition of a sound." I see it as the difference between "rain" and "raining". Hence "rain forest" and not "raining forest". Earthquake and not earthquaking. Cook book and not cooking book. Sunshine and not sunshining. Speech disorder and not speaking disorder. But apparently I am wrong? :-]