c.o.d. Cash (or collect) on delivery.
cog. Cognate.
Col. Colonel; Column; Colossians.
coll. College; Colleague; Collector; Colloquial.
collat. Collateral.
collect. Collective.
colloq. Colloquially.
Com. Commander; Commodore; Committee; Commissioner; Commonwealth.
com. Common; Comedy; Commerce; Commune.
comm. Commentary; Commander.