From Longman Dictionary of Contemporary Englishmuttmutt /mʌt/ noun [countable] informal HBADHPa dog that does not belong to any particular breed SYN mongrel
Examples from the Corpus
mutt• These drooling mutts get into all sorts of trouble during their free time on the streets.• More exciting and exotic is a dash across the tundra bundled on a dogsled between a musher and his muscular mutts.• He was Josh, the stray mutt.• Do you seriously believe the mutt tastes what it gulps down?• Anybody else would have put the mutt to sleep.• It was the usual mutt, old Fairman's, starting it all off.Origin mutt (1800-1900) muttonhead “stupid person” ((19-21 centuries)) 