Sentence:  During the next five years liberal leaders in the United States sank in the cumulative confusion attendant upon and manifested in a negative policy of Containment - and the <WSD>bitterest</WSD> irony - enforced and enforceable only by threat of a weapon that we felt the greatest distaste for but could not abandon : 
Meaning of the word marked with <WSD> tags:  harsh or corrosive in tone