ampere (symbol A) SI unit of electric current. It is defined as the current in a pair of straight, parallel conductors of infinite length and 1m (39in) apart in a vacuum that produces a force of 2 × 10⁻⁷ newton per metre in their length. This force may be measured on a current balance instrument, the standard against which current meters, such as an ammeter, are calibrated.

ampère unit of electric current. XIX. f. name of A. M. Ampère (d. 1836); adopted by the Congrès Électrique at Paris, 1881. abbrev. amp.

ampere (am-pair) n. the basic SI unit of electric current. It is equal to the current flowing through a conductor of resistance 1 ohm when a potential difference of 1 volt is applied between its ends. Symbol: A.