1. postage(n = noun.possession) - the charge for mailing something;
is a kind of charge
2. postage(n = noun.communication) postage stamp, stamp - a small adhesive token stuck on a letter or package to indicate that that postal fees have been paid;
is a kind of item, token
Derived form verb post11
The price established by law to be paid for the conveyance of a letter or other mailable matter by a public post. [1913 Webster]
postage, n. the amount charged for sending a letter etc. by post, usu. prepaid in the form of a stamp ({pound}25 including postage & packing).
Idiom:
postage meter US a franking-machine. postage stamp an official stamp affixed to or imprinted on a letter etc. indicating the amount of postage paid.