Both tags are about the
NSFetchedResultsController class in the Apple "Core Data" framework, and it is obvious that both tag names are different attempts to cope with the limit of 25 characters.
nsfetchedresultscontrolle has currently 780 questions and has a tag wiki, so this should be the "master".
nsfetchedresultcontroller has 83 questions and no wiki, so this should be the synonym.
(I proposed this already using the "suggest tag synonym" form, but the request is pending for 5 month now. Probably few people review the "pending request".)