dim
nonintelligent
unintelligent
dull
nonsmart
unsmart
lackluster
unsmartness
stupidass
unbright
vacancy
unintellectual
unclever
underbrained
gormless
ungroomed
half-witted
unintelligence
nonsavvy
stupid
ungeeky
short-witted
halfwit
not the sharpest tool in the shed
not the sharpest tool in the box
not the sharpest knife in the drawer
slow-witted
cerebrally challenged
intellectually challenged
unintellectualized
mindless
light-witted
vacuous
vacant
doltish
unastute
cloistered
ungenius
mentally challenged
unknowledgeable
simple-mindedly
sharp as a bowling ball
noninsightful
unskillful
fool
uninsightful
subintellectual
uncleverness
unreasonably
nonintellectual