Lexical Definition

‎μεσιτεύω‎ mesiteúō (mes-it-yoo'-o) to guarantee ^G:V
from ‎μεσίτης‎

confirm.

• to interpose (as arbiter), i.e (by implication) to ratify (as surety)

Abbott-Smith

* μεσιτεύω (< μεσίτης),
to interpose, mediate: ὅρκῳ, He 6:17 (MM, ii, iii).†

Abbott-Smith References

Liddell-Scott-Jones

μεσιτεύω-εύω,

act as arbiter or mediator, [Refs 1st c.AD+]; τισι [Refs 1st c.AD+]; μ. ὅρκῳ [NT]; act as go-between, τῇ Πασιφάῃ πρὸς τὸν ἔρωτα τοῦ ταύρου [Refs]

__2 transitive, mediate, negotiate, τὴν διάλυσιν μ. [Refs 2nd c.BC+]
__3 pledge, mortgage property, [Refs 1st c.AD+]
__4[Refs 1st c.AD+]
__5 add as a third constituent, χάλκανθον[Refs 5th c.BC+]
__II intransitive, τὰ χρήματα μ. lies on deposit with a stakeholder, [Refs 2nd c.BC+]
__II.2 lie between, μονάδος καὶ δεκάδος [Refs]

_{LSJ Scripture Refs: Heb.6.17}