dumb

dumb 1

•  adjective

1    old-fashioned unable to speak. Some people consider this to be offensive
2    informal, especially AmE stupid:
?What a dumb idea.
dumbly adverb

dumb 2
dumb down phrasal verb [T]
to change something in a way that has a very bad effect, by making it much too simple or much less effective:
?the dumbing down of TV news