duffer
[noun]
Synonyms: peddler, arab, hawker, higgler, huckster, monger, outcrier, packman, roadman, vendor, dunce, blockhead, boob, dimwit, dolt, dope, dumbbell, idiot, ignoramus, numskull

[TahlilGaran] English Synonym Dictionary ▲

duf‧fer /ˈdʌfə $ -ər/ noun [countable] informal
[Date: 1700-1800; Origin: Perhaps from Scottish English doofart 'stupid person']
someone who is stupid or not very good at something

[TahlilGaran] Dictionary of Contemporary English ▲