Dumber is the word used by people who are trying to be funny by making what sounds like a grammatically incorrect sentence while it actually is perfectly correct.
Dumber is the word you would use to describe your best friend Rava because she is a dumb a$$ bitch! She also likes to eet shreks azz. That why she is dumber. (dumber is pronounced like lumber)
OMG! Did you see that gorl named rava.. she is the definition of DUMBER!