1.  roundness(n = noun.communication) rotundity - the fullness of a tone of voice; "there is a musky roundness to his wordiness"
is a kind of tone, tone of voice
Derived form adjective round₂

2.  roundness(n = noun.attribute) - the quality of being round numbers; "he gave us the results in round numbers, but their roundness didn't affect the point he was making"
is a kind of figure, number
Derived form adjective round₃

3.  roundness(n = noun.attribute) - the property possessed by a line or surface that is curved and not angular;
is a kind of configuration, conformation, contour, form, shape
has particulars: globosity, globularness, rotundity, rotundness, sphericalness, sphericity, cylindricality, cylindricalness, circularity, disk shape
Antonym: angularity
Derived form adjective round₁

4.  roundness(n = noun.attribute) embonpoint, plumpness - the bodily property of being well rounded;
is a kind of corpulency, fleshiness, obesity
has particulars: chubbiness, pudginess, rolypoliness, tubbiness, buxomness

1.  The quality or state of being round in shape; as, the roundness of the globe, of the orb of the sun, of a ball, of a bowl, a column, etc. [1913 Webster]

2.  Fullness; smoothness of flow; as, the roundness of a period; the roundness of a note; roundness of tone. [1913 Webster]

3.  Openess; plainess; boldness; positiveness; as, the roundness of an assertion. [1913 Webster]

N  circularity, roundness, rotundity, circle, circlet, ring, areola, hoop, roundlet, annulus, annulet, bracelet, armlet, ringlet, eye, loop, wheel, cycle, orb, orbit, rundle, zone, belt, cordon, band, contrate wheel, crown wheel, hub, nave, sash, girdle, cestus, cincture, baldric, fillet, fascia, wreath, garland, crown, corona, coronet, chaplet, snood, necklace, collar, noose, lasso, lassoo, ellipse, oval, ovule, ellipsoid, cycloid, epicycloid, epicycle, semicircle, quadrant, sextant, sector, sphere, round, rounded, circular, annular, orbicular, oval, ovate, elliptic, elliptical, egg-shaped, pear-shaped, cycloidal, spherical, I watched the little circles die.

N  rotundity, roundness, cylindricity, sphericity, spheroidity, globosity, cylinder, cylindroid, cylindrical, barrel, drum, roll, roller, rouleau, column, rolling-pin, rundle, cone, conoid, pear shape, egg shape, bell shape, sphere, globe, ball, boulder, bowlder, spheroid, ellipsoid, oblong spheroid, oblate spheroid, prolate spheroid, drop, spherule, globule, vesicle, bulb, bullet, pellet, pelote, clew, pill, marble, pea, knob, pommel, horn, knot (convolution), curved surface, hypersphere, hyperdimensional surface, rotund, round, cylindric, cylindrical, cylindroid, columnar, lumbriciform, conic, conical, spherical, spheroidal, globular, globated, globous, globose, egg shaped, bell shaped, pear shaped, ovoid, oviform, gibbous, rixiform, campaniform, campanulate, campaniliform, fungiform, bead-like, moniliform, pyriform, bulbous, tres atque rotundus, round as an orange, round as an apple, round as a ball, round as a billiard ball, round as a cannon ball.