The article deals with various synonymic rows of phonetic terms, the main causes of synonymy. The source material was a series of works on Russian grammar, including the works of domestic linguists: M.V. Lomonosov, A.A. Barsov, N.G. Kurganov, A.H. Vostokov, N.I. Grech, G. Pavsky, K. Aksakov, V.A. Bogoroditsky, F.F. Fortunatov, I.A. Baudouin de Courtenay, A.A. Potebnya and others.