Sentence:  The Constitution of the Southern `` Confederation '' differed from that of the Federal Union only in two important respects : It openly , defiantly , recognized slavery - an institution which the Southerners of 1787 , even though they continued it , found so impossible to reconcile with freedom that they carefully avoided <WSD>mentioning</WSD> the word in the Federal Constitution . 
Meaning of the word marked with <WSD> tags:  make reference to