Real Dictionary

variable
adjective: Something that is variable changes quite often, and there usually seems to be no fixed pattern to these changes.

variable in American English
anything changeable; esp., a quality or quantity that varies or may vary
apt or likely to change or vary; changeable, inconstant, fickle, fluctuating, etc.
adjective: apt or liable to vary or change; changeable
noun: something that may or does vary; a variable feature or factor

variable in British English
adjective: liable to or capable of change
noun: something that is subject to variation

variable in Electrical Engineering
adjective: A variable electrical component or device is designed so that a particular property, such as resistance, can be varied.