Default, welsh (6)
I believe the answer is:
renege
I believe this clue is a double definition.
'default' is the first definition.
(I've seen this before)
'welsh' is the second definition.
(thesaurus)
(Other definitions for renege that I've seen before include "In card games, revoke" , "South American cowboy" , "Change one's mind" , "Go back (on promise etc)" , "Fail to keep promise, or revoke in cards" .)