conjugate base

Short definition from Wiktionary

Noun

1. 1
   Any compound, of general formula Xⁿ⁺, which can be transformed into a conjugate acid HX⁽ⁿ⁺¹⁾⁺ by the gain of a proton.
2. 2
   Any compound, of general formula Xⁿ⁺, which can be transformed into a conjugate acid HX⁽ⁿ⁺¹⁾⁺ by the gain of a proton: Such a base with enough basic activity to participate in its own equilibrium.