'eco-activist' originates from a combination: the prefix 'eco-' comes from Greek, specifically the word 'oikos', where 'oikos' meant 'house' (extended to mean environment in terms like 'ecology'), and 'activist' comes from modern English 'activist', ultimately from Latin 'activus' (from 'agere' meaning 'to do' or 'to act').

'eco-' entered English via scientific terms such as 'ecology' (from Greek via Latin and modern European languages) in the 19th century; 'activist' arose in the 20th century from 'active' + '-ist'. The compound 'eco-activist' emerged in late 20th century English to denote someone actively engaged in environmental activism.

Initially 'oikos' meant 'house' and 'activist' meant 'a person who takes action'; over time the compound came to mean specifically 'a person taking direct action for environmental protection'.