I have read this word quite often and always tried to elicit its meaning from the context and circumstances in which it was said.. More often than not I took it as a word for official ban or penalty.. until recently when I was watching an interview in which the interviewee felt offended over a question asked by someone in the audience and refused to answer it and said "she do not sanction impoliteness"...contextually meaning approval or consent. When I googled its meaning, it offered me two usages :-
a threatened penalty for disobeying a law or rule; syn- penalty, ban, deterrent, correction
official permission or approval for an action; syn- permission ,authority, agreement
Both of them are almost contradictory and do not offer an unambiguous understanding when used in sentence.
For example: the court sanctioned the proposal. Did the court approved or deterred?