Aho (あほ): Moron in the Kansai dialect. Could also be used to state an action is stupid.
Aikawarazu (相変わらず): As usual. The same as always.

Aite (相手): Opponent.

Aitsu (あいつ): Rude way of saying THAT person.

Akan (あかん): The Kansai way of saying “no use” or “no good.”

Akirameru (諦める): To give up.

Akuma (悪魔): Demon.

Arienai (有り得ない): Unbelievable. Impossible. In the Kansai dialect, this becomes ariehen.

Arubaito (アルバイト): Part time work. Sometimes shortened to baito. Derived from the German word arbeit.

Arukimasu (歩きます): Walk.

Ashi (足): Leg

Atarimae (当たり前): Of course. Naturally.

Atsui (熱い): Hot.

Ayamaru (謝る): To apologize.

Ayashii (怪しい): Suspicious

Baba (ばば): Old woman. The male version is jiji.

Baka (バカ): Stupid. Probably the most well-known rude Japanese swear word.

Bakemono (化物): Monster.

Benkyou (勉強): Study. To learn.

Betsu Ni (別に): It’s nothing. Nah.

Bijin (美人): Beauty.

Bikkuri Suru (びっくりする): To be shocked. Suru is often omitted.

Bimbo (貧乏): Poor. Lacking money. The opposite is kane mochi.

Bishounen (美少年): A beautiful young guy.

Bocchan (坊ちゃん): Occasionally used as a semi-derogative slang for rich boys.
Also, the title of one of Japan’s most famous novels.

Bouken (冒険): Adventure.

Bouzu (坊主): Small boy. The term actually means young monk but it came to be associated with young boys because young male Japanese students used to shave their heads bald.

… chatta (… ちゃった): This suffix is tagged to verbs to indicate something as done and irreversible. Could imply regret too.

Chibi (チビ): Small cute thing.

Chigau (違う): Wrong. In the Kansai dialect, this becomes chau.

Chiisai (小さい): Small.

Chikara (力): Strength.

Chinpira (チンピラ): Hoodlum.

Chotto Ii (ちょっといい): Do you have a moment?

Chou (超): A prefix meaning super.
Chousen (挑戦): Challenge.

Daijoubu (大丈夫): This means “fine/okay” and could be used in a variety of situations, including, “Are you daijoubu (fine) with that?”

Dakara (だから): Therefore.

Dame (駄目): Ineffective. No use. No good. Or simply, no.

… de gozaru/gozaimasu (…でござる/ございます): A highly formal, largely archaic way of ending a sentence. (Consider it the medieval form of … desu) Nowadays, often used in Anime for comedic effect. Such as to portray a character as unnaturally polite, or obsessed with medieval chivalry.

Dekkai (でっかい): Huge.

Densetsu (伝説): Legend. Densetsu no otoko. The legendary guy.

Deshi (弟子): Disciple.

Dete Ke (でてけ): Get out!

Doki Doki (ドキドキ): An onomatopoeia indicating the rapid thumping of one’s heart. Such as when seeing one’s absolute true love.
Don Don (どんどん): Progressively

Fukuzatsu (複雑): Complicated. The opposite is kan tan.

Fuzaken (ふざけん): A very rude way of saying, don’t mess with me. Often spat as
fuzakenna too.

Gaki (ガキ): Brat. Kid.

Giri Giri (ぎりぎり): Just in time. There are many such repeated words in the Japanese language, and linguistically, they are known as onomatopoeias.

Gyaru (ギャル): Hot babe.

Hakai Suru (破壊): To destroy

Hamon (破門): Excommunication. Expulsion from a clan or guide.

Hashiru (走る): Run.

Hayai (速い): Quick. Fast.

… hazu (… はず): Tagged to end of sentences to imply uncertainty.

Hazukashii (恥ずかしい): Embarrassing.

Heiki (平気): I’m fine.

Hentai (変態): Pervert. Abnormal.

Hidoi (ひどい): Awful. Terrible.