Lexical Definition

‎σύμφημι‎ sýmphēmi (soom'-fay-mee) to agree ^G:V
from ‎σύν‎ and ‎φημί‎

consent unto.

• to say jointly, i.e. assent to

Abbott-Smith

* σύν-φημι (Rec. συμ-),
to consent, confess: c. dat., seq. ὅτι, Ro 7:16.†

Abbott-Smith References

Liddell-Scott-Jones

σύμφημι,

future -φήσω[Refs 5th c.BC+]: aorist 1 συνέφησα [Refs]aorist 2 συνέφην frequently in [Refs 5th c.BC+]:—assent, approve, or agree fully, [Refs 5th c.BC+]

__2 with accusative of things, concede, agree to, grant, ταῦτα.. πάντες ἄρα συνέφασαν [Refs 5th c.BC+] (σοι) I grant you, [Refs 5th c.BC+]; frequently in Platonic dialogue, σύμφαθι ἢ ἄπειπε say yes or no,[Refs]
__3 with accusative et infinitive, agree that.., [Refs 5th c.BC+]; σ. τῷ νόμῳ ὅτι καλός, ={σ. τὸν νόμον καλὸν εἶναι}, [NT]
__4 with infinitive future, promise, [Refs 5th c.BC+]

_{LSJ Scripture Refs: Rom.7.16}