Sentence:  At once my ears were drowned by a flow of what I took to be Spanish , but - the driver 's white teeth flashing at me , the road wildly veering beyond his glistening hair , beyond his gesticulating bottle - it could have been the purest Oxford English I was half hearing ; I would n't have <WSD>known</WSD> the difference . 
Meaning of the word marked with <WSD> tags:  be cognizant or aware of a fact or a specific piece of information; possess knowledge or information about