'tegu' originates from Tupi–Guarani (or closely related indigenous languages of South America), specifically the word 'teju' or 'teyú', where the root meant 'lizard'.

'teju' (Tupi–Guarani) passed into Spanish and Portuguese as forms like 'teju'/'teiú' and was later adopted into English zoological and common usage as 'tegu'.

Initially, it meant simply 'lizard' in the indigenous language, but in English it came to denote specifically the large South American lizards of the Teiidae family now called 'tegus'.