dumber

As an adjective dumber

is (dumb).

As a verb dumben is

to make dumb.

As adjectives the difference between dumber and umber

is that dumber is (dumb) while umber is of a reddish brown colour, like that of the pigment.

As a noun umber is

a brown clay, somewhat darker than ochre, which contains iron and manganese oxides.

As an adjective dumber

is comparative of dumb.

As a verb dumbed is

past tense of dumb.

As a noun dumper

is a small one-man diesel-powered vehicle often used to carry loads and material around, often on building sites.

As an adjective dumber is

comparative of dumb.

As an adjective dumber

is (dumb).

As a verb cumber is

(dated) to slow down, to hinder, to burden.

As an adjective dumber

is (dumb).

As a noun dubber is

one who dubs, or gives a name.

As a noun lumber

is (uncountable) wood intended as a building material.

As a verb lumber

is to move clumsily.

As an adjective dumber is

(dumb).

As adjectives the difference between number and dumber

is that number is comparative of numb while dumber is comparative of dumb.

As a noun number

is an abstract entity used to describe quantity.

As a verb number

is to label (items) with numbers; to assign numbers to (items).