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 bitterest <WSD>irony</WSD> - 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:  incongruity between what might be expected and what actually occurs