1. Noun

   idiot; moron; fool

   Usually written using kana alone

   こんな荒れ模様の日に外出するなんて君は馬鹿だよ。

2. Na-adjective (keiyodoshi)

   stupid; foolish; dull; absurd; ridiculous

   Usually written using kana alone

3. Noun, Na-adjective (keiyodoshi)

   trivial; insignificant; disappointing

   Usually written using kana alone

4. malfunctioning; defective; losing sensation

   Usually written using kana alone

5. Noun, Noun, used as a prefix

   incredibly; unusually; exceptionally

   Usually written using kana aloneSlang

6. Noun, Noun, used as a suffix, Na-adjective (keiyodoshi)

   fervent enthusiast; nut; person singularly obsessed with something

   Usually written using kana aloneSlangusu. in compounds

7. Noun

   Mactra chinensis (species of trough shell)

   AbbreviationUsually written using kana alonesee 馬鹿貝

Also written 莫迦【ばか】