rotundity (n.)

"round, spherical, globular; rounded out, bulbous," 1705, from Latin rotundus "rolling, round, circular, spherical, like a wheel," from rota "wheel" (see rotary). Earlier was rotound (1610s); rotounde (early 15c.); rotundal (1620s), rotundious (1620s). In reference to a full-toned style of oratory by 1830, after Horace's ore rotundo in "Poetics," from the roundness of the mouth in pronouncing.