smooth mouthn. the worn teeth without cusps found in horses more than seven or eight years old.
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the world > animals > mammals > group Ungulata (hoofed) > family Equidae (general equines) > body or parts of horse > [noun] > mouth or type of > teeth > that indicate age
gnomons1607
shell-tooth1706
smooth mouth1940
1940 Chambers's Techn. Dict. 560/2Mouth, smooth (Vet.). Smooth and polished grinding surface of the molar teeth of horses.
1955 R. P. HobsonNothing too Good for Cowboy vi. 51 Between eight and ten years of age..they [sc. horses] acquire what we call a smooth mouth.