'tautology' originates from Greek, specifically the word 'tautologia', where 'tauto-' meant 'the same' and '-logia' (from 'logos') meant 'speech' or 'study'.

'tautology' changed from Greek 'tautologia' into Late Latin/'New Latin' 'tautologia', and then entered Middle/Modern English as 'tautology'.

Initially, it referred to 'saying the same thing' or 'the same wording repeated', but over time it came to include the current senses of 'redundant expression' in rhetoric and 'a universally true formula' in logic.