noun which may take the genitive case particle 'no', noun
undefeated; unbeatable; invincible
Describes a person, team, or record that has never been defeated or is considered impossible to defeat. Often used in sports, military, and competitive contexts.
That team boasts an undefeated record this season.
He is known as an unbeatable champion.
不敗 describes an actual undefeated record, while 無敵 describes an inherent quality of invincibility regardless of track record.
certain victory; invincibility
Compound of 不 (not) and 敗 (lose/be defeated). The kanji combination directly conveys the meaning of 'not losing'.