Oxford English dictionary follows the trends of language rather than setting them definitionally. They offer the "extremely" definition because the word gets misused so often, not because of any original meaning. One can argue the merits of whether a dictionary should include such misuses that have become commonplace but that's the direction they have opted to go.
In the same vein as this debate, OED considers irregardless to be a proper synonym for regardless.
Very tangentially related -- I keep hearing "disorientated" in the audio edition of The Economist (which is British).
It drives me bonkers. I'm cool with neologisms if they add value -- but a 400-year old[1] neologism that's merely a longer way to say something we already have a word for is still too young for me to consider valid.
> to a very great extent; extremely: chronically stupid drivers, she was chronically indecisive.
Whether it makes sense or not, the dictionary agrees with both options.