鈍

blockhead

becoming dull

thickheaded

thickheaded

to waver in one's resolution

The Power of Insensitivity (book by Junichi Watanabe)

blunt weapon

insensitive

sharp or blunt

blockhead

thickheaded

slow-footed

luck, steadfastness and patience (the three keys to achieving success)

obtuse triangle

to become blunt

to blunt

dull sound

uxoriousness

slow-witted

dark gray

grey tinged with green

dim-witted

obtuse (of the shape of a leaf)

obtuse angle

dark sleeper (species of sleeper goby, Odontobutis obscura)

dullness

loris

dull yellow

annealing

dull pain

becoming numb

to become less capable

stupidity

poverty dulls the wit

half-wit

to anneal

to become dim-witted

slow

blunt (e.g. sword)

dullard (gen. from not picking up on other people's feelings)

to become insensitive

dull

dull or blunt sword

stupid

local train

dull-witted

frustratingly slow

slowly

becoming dull (of a knife, one's wits, etc.)

jet black

imbecility

dull-witted