Pronunciation: (am'pēr, am-pēr'),[key] —n.Elect. the base SI unit of electrical current, equivalent to one coulomb per second, formally defined to be the constant current which if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed one meter apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per meter of length. Abbr.: A, amp. Also,am'père.