Definition of "tautology" in English

noun

1. (uncountable) Redundant use of words, a pleonasm, an unnecessary and tedious repetition.

   • It is tautology to say, "Forward Planning".

2. (countable) An expression that features tautology.

   • The expression "raze to the ground" is a tautology, since the word "raze" includes the notion "to the ground".

3. (countable, logic, propositional logic) A statement that is true for all truth values of its propositional variables.

4. (countable, logic, first-order logic) A statement that is true for all truth values of its Boolean atoms.