King James Bible Dictionary

(Gr. katatome; i.e., "mutilation"), a term used by Paul contemptuously of those who were zealots for circumcision (Philippians 3:2). Instead of the warning, "Beware of the circumcision" (peritome) i.e., of the party who pressed on Gentile converts the necessity of still observing that ordinance, he says, "Beware of the concision;" as much as to say, "This circumcision which they vaunt of is in Christ only as the gashings and mutilations of idolatrous heathen."

A term for circumcision.
Philippians 3:2

CONCISION, noun [Latin , to cut off.] Literally, a cutting off. Hence, In scripture, the Jews or those who adhered to circumcision, which, after our Saviors death, was no longer a seal of the covenant, but a mere cutting of the flesh.

Beware of dogs; beware of the concision Philippians 3:2.