Denshi Jisho — Online Japanese dictionary

どん dull; slow; stupid; dull-brained
Na-adjective, Noun 
のろ dull; slow; stupid; dull-brained
Na-adjective, Noun 
ぐどん stupidity; silliness
Na-adjective, Noun, Sensitive 
ちどん dull-witted
Na-adjective, Noun 
ちどん dullness; stupidity
Na-adjective, Noun 
りどん sharp or blunt; bright or foolish
Noun 
ろどん imbecility; stupidity
Noun 
なまくら 1: (Usually written using kana alone) blunt (e.g. sword); dull;
2: lazy; cowardly; good for nothing
Na-adjective 
うすのろ half-wit; fool; simpleton
Na-adjective, Noun 
しいにび jet black
Noun, Obscure term 
しいにぶ jet black
Noun, Obscure term 
運根 うんこんどん luck, steadfastness and patience (the three keys to achieving success)
Noun 

You can also

Look up kanji details for *鈍.

Try a Yahoo Jisho search for *鈍 .
Try a Goo Jisho search for *鈍 .
Try a Google search for *鈍 .