'argus' originates from Latin, specifically the proper name 'Argus', which itself comes from Greek 'Argos' (Ἄργος), the name of a mythological figure noted for many eyes.

'argus' entered English via Latin and Middle English from the Greek mythological name 'Argos' (Ἄργος); over time the proper name was extended to common nouns (e.g. a watchful guardian, names of insects).

Initially, it referred specifically to the mythological many‑eyed figure 'Argus'; over time it evolved to mean 'a very watchful guardian' and has also been applied to certain insects (butterflies/moths) and figurative uses.