dull, slow, foolish, blunt
鈍 centers on a lack of sharpness or quickness: something dull, blunt, slow, or mentally sluggish. The meanings extend naturally from physical bluntness to slow-wittedness.
鈍 combines 金 (metal) with 屯, which likely contributes the sound and suggests something thick or blunt. The idea is metal that is not sharp.
Metal 金 that is thick and blunt 屯: a dull blade that cuts slowly, if at all.
For ドン, imagine a dull blade that goes 'don' with a heavy, slow thud instead of slicing cleanly: don -> ドン.
dull (e.g. a knife); blunt
thickheaded; obtuse; stupid
thickheaded; insensitive; dull; thick-skinned
to become blunt; to grow dull
dull; slow; stupid; dull-brained
blunt weapon
becoming dull; slowing down
stupid; dim-witted; dense; dull; obtuse; slow
local train; slow train
dull pain
blunt (e.g. sword); dull
thickheaded; slow-witted; phlegmatic; stolid; bovine
dark sleeper (species of sleeper goby, Odontobutis obscura)
dark gray; dark grey
sharp or blunt; bright or foolish
to become insensitive; to become less perceptive; to lose one's touch; to get out of practice
uxoriousness; being easy on one's wife; man who is easy on his wife
jet black
to waver in one's resolution
annealing