obtuse
blunt
dullery
wooden-headed
blockish
barren
poky
benumb
loggerheaded
blunt-witted
mindless
vacant
vacuous
duncery
dull-headed
half-witted
underwitted
doltish
flatness
ungenius
vacancy
unintelligence
room-temperature IQ
cerebrally challenged
unbright
dim-headed
dough-baked
intellectually challenged
dull
not the sharpest tool in the box
insipidness
insipidity
not the sharpest tool in the shed
boringness
dreariness
lackluster
not the sharpest knife in the drawer
unskillfulness
short-witted
thick-skulled
nondiligence
blah
dullwittedness
dullness
dull-witted
skillessness
slow-witted
simplicity
light-witted
Boeotian