arrested
artless
babbling
backward
blithering
bluff
blunt
born yesterday
burbling
candid
childlike
confiding
crackbrained
cracked
crazy
cretinistic
cretinous
dim-witted
direct
dithering
driveling
drooling
dull
feebleminded
frank
guileless
half-baked
half-witted
idiotic
imbecile
imbecilic
ingenu
ingenuous
innocent
maundering
mentally defective
mentally deficient
mentally handicapped
mentally retarded
mongoloid
moronic
naive
not all there
open
openhearted
outspoken
plain
retarded
simple
simplehearted