Sentence:  <WSD>At</WSD> 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 known the difference . 
Meaning of the word marked with <WSD> tags:  without delay or hesitation; with no time intervening