Lexical Definition

‎ἐκλανθάνομαι‎ eklanthánomai (ek-lan-than'-om-ahee) to forget ^G:V
middle voice from ‎ἐκ‎ and ‎λανθάνω‎

forget.

• to be utterly oblivious of

Abbott-Smith

** ἐκ-λανθάνω [in Sm.: Ps 13:2* * ;]
to escape notice utterly; mid., to forget utterly: He 12:5.†

Abbott-Smith References

Liddell-Scott-Jones

ἐκλανθάνω,

escape notice utterly:—middle, forget utterly, with genitive of things, ἐκ χόλω τῶδε λαθοίμεθα [Refs 7th c.BC+]; τοῦδ᾽ ἐκλανθάνει thou forgettest this entirely, [Refs 5th c.BC+]

__II causal in present ἐκληθάνω, with aorist 1 ἐξέλησα, Aeolic dialect ἐξέλᾱσα (see. below): Epic dialect reduplicate aorist 2 ἐκλέλᾰθον:
__II.1 active, make one quite forgetful of a thing, c.genitive of things, ἐκ δέ με πάντων ληθάνει ὅσσ᾽ ἔπαθον [Refs 8th c.BC+] with accusative _of things_, ἐκλέλαθον κιθαριστύν made him quite forget his harping, [Refs 8th c.BC+]
__II.2 middle and passive, forget utterly, ὀϊζύος ἐκλελαθέσθαι [Refs 8th c.BC+]: with infinitive, ἐκλάθετο..καταβῆναι [Refs 8th c.BC+]