late 14c., of persons, "apt to change, fickle," from Old French variable "various, changeable, fickle," from Late Latin variabilis "changeable," from variare "to change" (see vary). Of weather, seasons, etc., attested from late 15c.; of stars, from 1788.
"quantity that can vary in value," 1816, from variable (adj.) in mathematical sense of "quantitatively indeterminate" (1710). Related: Variably; variability.