How do you say dumb in spanish?

In spanish everything needs a gender. As in boy and girl o means boy and a means girl. ( o and a at the end of the Word means if it's a boy or girl) So tonto means dumb in boy form as if your calling a boy dumb because of the o. and tonta means dumb in girl form. So I say El tonto chico means the stupid/silly boy If i say La tonta chica means the stupid/silly girl. La and el means the. the e in the means masculine to and the a in the means feminine so you should look at that to see what gender it is.

English: Dumb

Spanish: Tonto