負ける:まける: lose a game or fight or struggle.

 参った:まいった: (spoken aloud) to say uncle. "no mas!"

 敗北:はいぼく: a loss of a game or war (noun)

 失敗:しっぱい: any failure! test, your plan fails, no one comes to your party, your business goes bankrupt.

 失う:うしなう:  to miss out on something (but not because of an opponent). Like you slept too late and missed your TV show.

 不合格:ふごうかく: unacceptable! (used with schoolwork, but also work reviews, or 'this workmanship is unacceptable' or 'Son your room is not acceptably clean.')

 落第:らくだい: to fail a test