daff
Daff (noun) means a silly or stupid person.
Etymology
This word came into English from Middle English daf, daffe ("fool, idiot"), which developed from Old Norse daufr ("deaf, stupid"), itself from Proto-Germanic *daubaz ("deaf, stunned"), going back further to Proto-Indo-European *dʰewbʰ- ("to whisk, whirl, smoke, be obscure"). It is a doublet of deaf, dof and dowf, and is cognate with Swedish döv ("deaf") and Danish døv ("deaf, stupid"). See also deaf.