愚鈍[gudon] stupidity
神経の鈍い[shinkeinonibui] insensitive
鈍い[osoi] slow
鈍化[donka] becoming dull
鈍角[donkaku] obtuse angle

鈍感[donkan] thickheadedness
鈍間[noroma] blockhead
鈍器[donki] blunt weapon
鈍行[donkou] ordinary train
鈍臭い[donkusai] slow (opposite of fast)