Answer: nag

AnswerCrossword Clue
NAGBadger
NAGGripe on and on
NAGCarp at
NAGNo Derby winner
NAGPlague
NAGOld workhorse
NAGRacehorse, slangily
NAGWhat Walter Mitty's wife tends to do
NAGConsistently pester
NAGWalter Mitty's wife, e.g.
NAGConstantly find fault
NAGGripe constantly
NAGBadger or hound
NAGPick on
NAGFaultfinder
NAGScraggly horse
NAGBother a lot
NAGFind fault with, to a fault
NAGWhiner
NAGNudge
nagperson who nags
NAGMount over the hill
NAGWorthless horse
NAGFuss at
NAGGet on someone's case
NAGHarry
NAGHenpeck
NAGOld horse or ex-wife
NAGPester
NAGRemind and remind and remind
NAGAnnoy
NAGHarp
NAGHound or horse
NAGHorse that's had it
NAGRosinante
NAGComplain and complain
NAGGlue-factory candicate
NAGSwaybacked sort
NAGKvetch
NAGWorry or bother