Undefeated means never having lost. An undefeated season, retire undefeated, still undefeated.
It is the plainest praise in sport and needs no adjective beside it. Retiring undefeated is rare enough to be famous when it happens, since almost everybody stays one fight or one season too long.
1adjectiveundefeatedNever having lost.
“The team stayed undefeated all season and won the league easily.”
undefeated is a record.
From un- + defeated.
Etymology from Wiktionary, CC BY-SA