1.  variable(n = noun.object) - something that is likely to vary; something that is subject to variation; "the weather is one variable to be considered"
Derived form adjective variable₁

2.  variable(n = noun.cognition) variable quantity - a quantity that can assume any of a set of values;

3.  variable(n = noun.object) variable star - a star that varies noticeably in brightness;

4.  variable(n = noun.communication) - a symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity;

1.  variable(a = adj.all) - liable to or capable of change; "rainfall in the tropics is notoriously variable"; "variable expenses"; "variable winds"
Antonym: invariable
Derived form noun variability₁, noun variable₁, noun variableness₁, verb vary₁, verb vary₃

2.  variable(s = adj.all) varying - marked by diversity or difference; "nature is infinitely variable"; "the varying angles of roof slope"
Derived form noun variability₂, noun variableness₁, verb vary₁, verb vary₃, verb vary₄

3.  variable(s = adj.all) - (used of a device) designed so that a property (as e.g. light) can be varied; "a variable capacitor"; "variable filters in front of the mercury xenon lights"
Derived form noun variability₁, noun variableness₁

1.  Having the capacity of varying or changing; capable of alternation in any manner; changeable; as, variable winds or seasons; a variable quantity. [1913 Webster]

2.  Liable to vary; too susceptible of change; mutable; fickle; unsteady; inconstant; as, the affections of men are variable; passions are variable. [1913 Webster]

1.  That which is variable; that which varies, or is subject to change. [1913 Webster]

2.  A quantity which may increase or decrease; a quantity which admits of an infinite number of values in the same expression; a variable quantity; as, in the equation x2 - y2 = R2, x and y are variables. [1913 Webster]

3.  A shifting wind, or one that varies in force. [1913 Webster]

variable, adj. & n.
--adj.
1 a that can be varied or adapted (a rod of variable length; the pressure is variable). b (of a gear) designed to give varying speeds.
2 apt to vary; not constant; unsteady (a variable mood; variable fortunes).
3 Math. (of a quantity) indeterminate; able to assume different numerical values.
4 (of wind or currents) tending to change direction.
5 Astron. (of a star) periodically varying in brightness.
6 Bot. & Zool. (of a species) including individuals or groups that depart from the type.
7 Biol. (of an organism or part of it) tending to change in structure or function.
--n.
1 a variable thing or quantity.
2 Math. a variable quantity.
3 Naut. a a shifting wind. b (in pl.) the region between the NE and SE trade winds.

Derivative:
variability n. variableness n. variably adv.

Etymology:
ME f. OF f. L variabilis (as VARY)

N  irregularity of recurrence, irregularity, uncertainty, unpunctuality, fitfulness, capriciousness, ecrhythmus, irregular, uncertain, unpunctual, capricious, desultory, fitful, flickering, rambling, rhapsodical, spasmodic, immethodical, unmethodical, variable, irregularly, by fits and starts.

N  changeableness, mutability, inconstancy, versatility, mobility, instability, unstable equilibrium, vacillation, fluctuation, vicissitude, alternation, restlessness, fidgets, disquiet, disquietude, inquietude, unrest, agitation, moon, Proteus, chameleon, quicksilver, shifting sands, weathercock, harlequin, Cynthia of the minute, April showers, wheel of Fortune, transientness, changeable, changeful, changing, mutable, variable, checkered, ever changing, protean, proteiform, versatile, unstaid, inconstant, unsteady, unstable, unfixed, unsettled, fluctuating, restless, agitated, erratic, fickle, irresolute, capricious, touch and go, inconsonant, fitful, spasmodic, vibratory, vagrant, wayward, desultory, afloat, alternating, alterable, plastic, mobile, transient, wavering, seesaw, off and on, a rolling stone gathers no moss, pictra mossa non fa muschis, honores mutant mores, varium et mutabile semper femina.