Sentence:  Each day too slew it'ssic thousands six or seven,/ Till at the crowning carnage—Waterloo—/ They threw their pens down in divine disgust,/ The page was so besmeared with blood and dust. […]/ (Here, Sathan's sole good work deserves insertion—/ 'Tis, that he has both Generals in <WSD>reversion</WSD>). 
Meaning of the word marked with <WSD> tags:  The return of an estate to the donor or grantor after expiry of the grant.