Sentence:  So cam he to the chamber dore / and wold haue entryd / And anone a voyce said to hym / Flee launcelot / and entre not / for thou oughtest not to doo hit / And yf thou entre / thou shalt <WSD>forthynke</WSD> hit / Thenne he withdrewe hym abak ryght heuy<!--Prior quote:‘Sir Launcelot, flee and entir nat, for thou ought nat to do hit, for and if thou entir, thou shalt <WSD>forthynke</WSD> hit.'--> 
Meaning of the word marked with <WSD> tags:  To regret.