'pet-toxic' originates from Modern English, formed by combining 'pet' (from Middle English 'pet', meaning 'tame animal' or 'domestic animal') and 'toxic' (from Greek 'toxikon' via Latin 'toxicum', meaning 'poison').

'toxic' entered English via Latin 'toxicum' and Old French 'toxique' and developed into the Modern English adjective 'toxic'; 'pet' has been used in English since Middle English to mean a tame or domesticated animal. The compound 'pet-toxic' is a relatively recent, descriptive formation (20th–21st century) created to specify toxicity affecting pets.

Initially, 'toxic' meant 'poisonous' and 'pet' meant 'tame/domestic animal'; over time the combined expression 'pet-toxic' evolved to specifically mean 'poisonous or harmful to pets' in warnings, labels, and consumer information.