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 <WSD>reconcile</WSD> with freedom that they carefully avoided mentioning the word in the Federal Constitution . 
Meaning of the word marked with <WSD> tags:  make (one thing) compatible with (another)