Extended Strong's Greek Lexicon (Abbott-Smith based)
untrustworthy
Usage: ἀ-σύν-θετος, -ον (συντίθεμαι ν. M, Pr., 222; MM, see word), [in LXX: Jer.3:7-11 (בָּגַד)* ;] false to engagements, not keeping covenant, faithless (MM, see word): Rom.1:31.† (AS)