Sentence:  there came fourty knyghtes to sire Darras /.../ and they wold haue slayne sire Tristram and his two felawes / but sire Darras wold not suffre that but kepte them in pryson /.../ So sire Tristram endured there grete payne / for sekenesse had <WSD>vndertake</WSD> hym / and that is the grettest payne a prysoner maye haue<!--Prior quote:So Sir Trystram endured there grete payne, for syknes had <WSD>undirtake</WSD> hym&mdash;and that ys the grettist payne a presoner may have--> 
Meaning of the word marked with <WSD> tags:  To take by trickery; to trap, to seize upon.