Sentence:  It was a <WSD>casual</WSD> sneer, obviously one of a long line. There was hatred behind it, but of a quiet, chronic type, nothing new or unduly virulent, and he was taken aback by the flicker of amazed incredulity that passed over the younger man's ravaged face. 
Meaning of the word marked with <WSD> tags:  Happening or coming to pass without design.