noun

a very stupid or glaring mistake, especially an amusing one.

the occasional schoolboy howler would amuse the examiners

mistake,error,blunder,fault,gaffe,slip,slip of the pen,lapsus calami,slip-up,boo-boo,boner,botch,fluff,fail,boob,bloomer,clanger,blooper,bloop,goof,malapropism,solecism,fuck-up