Sentence:  It was a casual sneer, obviously one of a long line. There was hatred behind it, but of a quiet, chronic type, nothing new or unduly <WSD>virulent</WSD>, 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:  Hostile to the point of being venomous; intensely acrimonious.