A sole sufficient operator or a sole sufficient connective is an operator that is sufficient by itself to define all of the operators in a specified set of operators.

In logical contexts this refers to a logical operator that suffices to define all of the boolean-valued functions, f : X → 𝔹, where X is an arbitrary set and where 𝔹 is a generic 2-element set, typically 𝔹 = {0, 1} = {false, true}, in particular, to define all of the finitary boolean functions, f : 𝔹^k → 𝔹.