Sanction is a noun which has two directly opposite meanings, which makes it a auto-antonym or contronym (i.e., a word that can contradict itself).
One meaning of sanction is to grant official endorsement or approval for an action.
The other meaning is the process taking by the international community against a specific country to force said country to comply with international law. These sanctions can include reducing or restricting trade or economic aid. Outside of international law, the word sanction may mean the penalty given for breaking a law.
As a verb, the meaning changes slightly. It means to make something official, legal, binding, or valid.
The adjective form is sanctionable or the very rare sanctionative.