Sanction is an unusual ambiguous word to me. In some cases it means to approve some action, while in other cases it means to prohibit or punish some action; and there being near opposite meanings, context is especially essential for correct interpretation.
What is interesting to me is: historically, how did sanction come to capture two opposite meanings like this? The etymology seems to trace back to the single Latin word sanctio, meaning a decree. But did sanctio have strong opposing meanings or connotations like our modern word sanction? Or how and when did the divergence occur over time?
Best Answer
What's happened is that the verb to sanction has retained the original sense relating to endorsement/recognition by official decree.
But the noun sanctions (invariably pluralised, frequently imposed or applied) has come to mean measures taken by authority (often, multiple cooperating authorities) to discourage unsanctioned activities. By default, it's usually governments restricting trade in certain goods and services with some other nation, in order to put pressure on its government.
There is also the "positive" singular noun give (ones) sanction, but as that link shows, it's rapidly declined as the "negative" plural noun impose sanctions has gained currency.
Although superficially this looks odd, in practice there's unlikely to be any confusion because the verb / plural noun distinction is almost always made.
Having said all that, usage does change. Increasing numbers of younger speakers rarely hear the verb or singular noun form with positive associations, and they effectively "back-form" a new verb form they want to mean to impose sanctions. @Jay has identified a few such usages already in "print", and much as they make me cringe, doubtless there will be more in future.