Quick Definition
ἰός, οῦ, ὁ n.m. poison, rust
Strong's Definition
perhaps from eimi (to go) or hiemi (to send); rust (as if emitted by metals); also venom (as emitted by serpents)
KJV Usage: poison, rust
UBS Dictionary of the Greek New Testament
noun, m. | -οῦ | κατιόομαι
8.74 · Body, Body Parts, and Body Products · Physiological Products of the Body
venom, poison (used especially of the venom of snakes) the poisonous secretion of some animals
2.60 · Natural Substances · Metals
rust, tarnish the substance resulting from the slow oxidation of metals (rust in the case of iron and tarnish in the case of gold and silver) Pure gold is not affected significantly by oxidation, but much of the gold of the ancient world was not pure, and therefore oxidation and resulting tarnish did take place. However, in most languages it is inappropriate to speak of ‘rust’ as occurring with gold and silver. If there is no satisfactory term to indicate the deterioration in gold and silver resulting in extreme tarnish, it may be possible to translate JAS 5:3 as ‘your gold and silver will be ruined and this will serve as a witness against you.’
UBS Dictionary of the Greek New Testament © United Bible Societies, licensed CC BY-SA 4.0.
Thayer's Greek Lexicon
ἰός, -οὔ, 6, (on its very uncert. deriv. see Kreussler in Passow s. v.; Curtius § 591; [Vaniéek p. 9697); 1. poison (of animals): ἰὸς ἀσπίδων ὑπὸ τὰ χείλη αὐτῶν, the poison of asps is under their lips, spoken of men given to reviling and calumniating and thereby injuring others, Ro. ili. 13 (fr. Ps. exxxix. (exl.) 3 (4)); by the same fig. (γλῶσσα) μεστὴ ἰοῦ θανατηφόρου, Jas. iii. 8; (in Grk. writ. fr. Pind. down). 2. rust: Jas. ν. 3; (Ezek. xxiv. 6.11 sq.; Bar. vi. [Ep. Jer.] 11 (12), 23 (24); Theogn., Theoer., Plat., Theophr., Polyb., Leian., al.).
Mounce Concise Greek Dictionary
ἰός ios 3x
a missile weapon, arrow, dart; venom, poison, Rom. 3:13; Jas. 3:8; rust, Jas. 5:3*
Abbott-Smith Greek Lexicon
ἰός, -οῦ, ὁ,
[in LXX: Ez 24:6, 11, 12 (חֶלְאָה), Ps 139 (140):3 (חֵמָה), al.;]
an arrow.
rust (Ez 24:6): Ja 5:3 (cf. MM, Exp., xv).
poison: fig., Ro 3:13 (Ps 139 (140):3), Ja 3:8.†
Moulton & Milligan — Vocabulary of the Greek NT
ἰός. Syl 587*° (B.c. 329) σίδηρος καταβεβρωμένος ὑπὸ τοῦ ἰοῦ illustrates the special sense of ‘‘ rust,” found in Jas 53: cf. 2. 139} (iii/B.C.) ὅπως δὲ καθαρὸς [t]od ἔσται ὁ ἀνδρίας + + » ἐπιμελεῖσθαι τοὺς ἀγορανόμους. The more general (δραχμὴ) a, similarly 57, in medical prescriptions for the eyes. As against Grimm’s ‘‘very uncert. deriv.” the word is obviously cognate with the Latin virus (Zend vis, visa-, skr. visam : see Boisacq, p- 379). >
Liddell-Scott-Jones — Greek-English Lexicon
ἰός (ios) — poison/rust. ἰός [ῑ], ὁ,
__C rust on iron, or verdigris on copper and bronze, [Refs 7th c.BC+]; patina on bronze statues, ὅπως καθαρὸς ἰοῦ ἔσται ὁ ἀνδριάς [Refs 5th c.BC+]