1.  arc(n = noun.phenomenon) discharge, electric arc, electric discharge, spark - electrical conduction through a gas in an applied electric field;
is a kind of electrical conduction
has particulars: brush discharge, corona, corona discharge, corposant, electric glow, saint elmo's fire, saint elmo's light, saint ulmo's fire, saint ulmo's light, st. elmo's fire, flashover

2.  arc(n = noun.shape) - a continuous portion of a circle;
is a kind of curve, curved shape
is a part of circle, sector
has particulars: limb
Derived forms verb arc₁, adjective arcuate₁

3.  arc(n = noun.shape) bow - something curved in shape;
is a kind of curve, curved shape
has particulars: rainbow
Derived form verb arc₁

   arc(v = verb.motion) arch, curve - form an arch or curve; "her back arches"; "her hips curve nicely"
is one way to bend, flex
Derived forms noun arc₂, noun arc₃
Sample sentences: Something ----s; Somebody ----s something

1.  A portion of a curved line; as, the arc of a circle or of an ellipse. [1913 Webster]

2.  A curvature in the shape of a circular arc or an arch; as, the colored arc (the rainbow); the arc of Hadley's quadrant. [1913 Webster]

3.  An arch. [1913 Webster]
"Statues and trophies, and triumphal arcs." [1913 Webster]

4.  The apparent arc described, above or below the horizon, by the sun or other celestial body. The diurnal arc is described during the daytime, the nocturnal arc during the night. [1913 Webster]

   To form a voltaic arc, as an electrical current in a broken or disconnected circuit. [Webster 1913 Suppl.]

arc, abbr.
1 (in the UK) Agricultural Research Council.
2 Aids-related complex.

arc, n. & v.
--n.
1 part of the circumference of a circle or any other curve.
2 Electr. a luminous discharge between two electrodes.
--v.intr. (arced; arcing) form an arc.

Idiom:
arc lamp (or light) a light source using an electric arc. arc welding a method of using an electric arc to melt metals to be welded.

Etymology:
ME f. OF f. L arcus bow, curve

N  curvature, curvity, curvation, incurvature, incurvity, incurvation, bend, flexure, flexion, flection, conflexure, crook, hook, bought, bending, deflection, deflexion, inflection, inflexion, concameration, arcuation, devexity, turn, deviation, detour, sweep, curl, curling, bough, recurvity, recurvation, sinuosity, kink, carve, arc, arch, arcade, vault, bow, crescent, half-moon, lunule, horseshoe, loop, crane neck, parabola, hyperbola, helix, spiral, catenary, festoon, conchoid, cardioid, caustic, tracery, arched ceiling, arched roof, bay window, bow window, sine curve, spline, spline curve, spline function, obliquity, curved, curviform, curvilineal, curvilinear, devex, devious, recurved, recurvous, crump, bowed, vaulted, hooked, falciform, falcated, semicircular, crescentic, sinusoid, parabolic, paraboloid, luniform, lunular, semilunar, conchoidal, helical, double helical, spiral, kinky, cordiform, cordated, cardioid, heart shaped, bell shaped, boat shaped, crescent shaped, lens shaped, moon shaped, oar shaped, shield shaped, sickle shaped, tongue shaped, pear shaped, fig shaped, kidney-shaped, reniform, lentiform, lenticular, bow-legged, oblique, circular, aduncated, arclike, arcuate, arched, beaked, bicorn, bicornuous, bicornute, clypeate, clypeiform, cymbiform, embowed, galeiform, hamate, hamiform, hamous, hooked, linguiform, lingulate, lobiform, lunate, navicular, peltate, remiform, rhamphoid, rostrate, rostriferous, rostroid, scutate, scaphoid, uncate, unguiculate, unguiform.

arc cosecant, arc cosine, arc cotangent, arc lamp, arc light, arc secant, arc sine, arc tangent, carbon arc, carbon arc lamp, electric arc, joan of arc, minute of arc, reflex arc