1610s, from Latin sonorus "resounding," from sonor "sound, noise," from sonare "to sound, make a noise," "to sound," from PIE *swene-, from root *swen- "to sound." Related: Sonorously; sonorousness. Earlier was sonouse (c. 1500), from Medieval Latin sonosus; sonourse "having a pleasing voice" (c. 1400), from sonor + -y (2).
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