ἰός

From Proto-Hellenic *ihwós, a thematicization of Proto-Indo-European *(H)isu- (“arrow”). Cognates include Sanskrit इषु (íṣu, “arrow”) and Avestan 𐬌𐬱𐬎 (išu, “arrow”).

ῑ̓ός • (īós) m (genitive ῑ̓οῦ); second declension

1. arrow
   • 800 BCE – 600 BCE, Homer, Iliad 1.48:

     ἕζετ’ ἔπειτ’ ἀπάνευθε νεῶν, μετὰ δ’ ἰὸν ἕηκε

     hézet’ épeit’ apáneuthe neôn, metà d’ iòn héēke

     Then he sat down apart from the ships and let fly an arrow.

Heteroclitic neuter plural:

From Proto-Hellenic *wihós, from Proto-Indo-European *wisós (“fluidity, slime, poison”). Cognates include Sanskrit विष (víṣa), Latin vīrus, Tocharian A wäs, Tocharian B wase, and Middle Irish fí.

ῑ̓ός • (īós) m (genitive ῑ̓οῦ); second declension

1. poison, venom
   • :

     καὶ μὴ τυχοῦσαι πράγματος νικηφόρου, χώρᾳ μεταῦθις ἰὸς ἐκ φρονημάτων πέδοι πεσὼν ἄφερτος αἰανὴς νόσος

     kaì mḕ tukhoûsai prágmatos nikēphórou, khṓrāi metaûthis iòs ek phronēmátōn pédoi pesṑn áphertos aianḕs nósos

     And if they fail to win their cause, the venom from their resentment will fall upon the ground, an intolerable, perpetual plague afterwards in the land.

• Greek: ιός m (iós, “venom”)

Uncertain. May be of the same origin as Etymology 2.

ῑ̓ός • (īós) m (genitive ῑ̓οῦ); second declension

1. rust, verdigris
   • 380 BCE, Plato, The Republic 609a:

     κακὸν ἑκάστῳ τι καὶ ἀγαθὸν λέγεις; οῖον ὀφθαλμοῖς ὀφθαλμίαν χαλκῷ δὲ καὶ σιδήρῳ ἰόν

     kakòn hekástōi ti kaì agathòn légeis? oîon ophthalmoîs ophthalmían khalkōî dè kaì sidḗrōi ión

     Do you say that there is for everything its special good and evil, as for the eyes ophthalmia and for bronze and iron rust?

Expansion of original feminine-only pronoun ἴᾱ (íā), from *(h₁)éy.

ῐός • (ĭós) m (feminine ῐ̓́ᾰ, neuter ῐ̓όν); first/second declension

1. selfsame; identical