Lexical Definition

‎σήπω‎ sḗpō (say'-po) to rot ^G:V
apparently a primary verb

be corrupted.

• to putrefy, i.e. (figuratively) perish

Abbott-Smith

σήπω [in LXX; Ps 37 (38):5* (מקק ni.), Jb 33:21 (כּלה) 40:7, Si 14:19, al. ;]
to make corrupt: 2 pf. act, with mid, sense (v. M, Pr., 154), σέσηπεν, has perished, become corrupted, Ja 5:2.†

Abbott-Smith References

Liddell-Scott-Jones

σήπω,

[Refs 5th c.BC+]: future σήψω [Refs 4th c.BC+]aorist ἔσηψα (δι-) [Refs 2nd c.AD+]:—make rotten or putrid, [Refs 4th c.BC+].with; of a serpent's poison, [Refs 4th c.BC+].with; of the sting of the σήψ, [Refs 2nd c.AD+]

__b soak hides, δέρματα σ. [Refs 5th c.BC+]
__2 metaphorically, corrupt, waste, αἱ ἡσυχίαι σήπουσι καὶ ἀπολλύασι [Refs 5th c.BC+]
__II mostly in passive (perfect σέσηπα being used in passive sense, [Refs 8th c.BC+], future σᾰπήσομαι [Refs 5th c.BC+]aorist ἐσάπην [ᾰ] [Refs 8th c.BC+]; σαπήῃ (κατα-), Epic dialect subjunctive for σαπῇ, [Refs 8th c.BC+]perfect σέσημμαι probably in [Refs 3rd c.AD+]:—rot, moulder, of dead bodies, χρὼς σήπεται [Refs 8th c.BC+]; of wood, δοῦρα σέσηπε [Refs 8th c.BC+]
__II.2 of live flesh, mortify, ὁ μηρὸς ἐσάπη [Refs 5th c.BC+]; promote coction or formation of 'laudable' pus, in active, [Refs 5th c.BC+]
__II.3 of water, [Refs 5th c.BC+]
__II.4 of the food rejected after digestion, [Refs 4th c.BC+]
__II.5 metaphorically, σ. ὑπὸ τῆς ἡδονῆς [NT+4th c.BC+]

_{LSJ Scripture Refs: Jas.5.2}