forthink

To cause distress or regret to; cause to regret or repent; to vex.

with hys swerd lyghtly he smote of hir hede before kynge Arthur / allas for shame sayd Arthur why haue ye done so / ye haue shamed me and al my Courte / for this was a lady that I was be holden to / and hyther she came vnder my sauf conduyte / I shalle neuer foryeue you that trespas / Sir said Balen me forthynketh of your displeasyr / for this same lady was the vntruest lady lyuynge

To regret; repent.

To regret.

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 forthynke hit / Thenne he withdrewe hym abak ryght heuy

To repent, be sorry for.

To change one's mind about; to renounce.

Then gan he thinke, perforce with sword and targe / Her forth to fetch, and Proteus to constraine; / But soone he gan such folly to forthinke againe.