> But some commonly used words are confusing. Sanction means both to allow and to disallow.

Well, technically, it means to allow or to punish. But you're close enough. It does have these two senses, they are obviously in tension with each other, and both are common.

But, because both senses are common, this isn't a source of confusion. (And the later sense of punishment did not arise from confusion on the part of speakers, as is the case for nonplussed.)