dull
dim
unbright
gormless
nonintelligent
blockish
unintelligent
not the sharpest tool in the box
not the sharpest knife in the drawer
not the sharpest tool in the shed
underwitted
lunky
slow-witted
half-witted
doltish
cloistered
nonsavvy
short-witted
lackluster
dull-minded
unknowledgeable
unsmart
vacancy
stupidass
subintellectual
dense
simple
halfwit
simpleton
unsmartness
submoron
four oh four
underbrained
ungenius
cerebrally challenged
dull-witted
intellectually challenged
mentally challenged
light-witted
sap
lackbrain
simple-mindedly
simplicity
unintelligence
uncomprehending
slow on the uptake
shitbrained
brainless
stun
Boeotian