adjective
dumber; -est
informal
not showing or having good judgment or intelligence :stupid or foolish
not requiring or resulting from intelligence
not able to speak especially after being shocked or surprised
b old-fashioned + often offensive :not having the ability to speak
verb
dumbs; dumbed; dumbing
dumb down
[phrasal verb]
dumb down (something) or dumb (something) down usually disapproving
to make (something) easier to understand
to make (a group of people) less intelligent or educated