complete, comprehensive (esp. BrE), decisive, heavy, major, overwhelming, resounding, serious, stunning, total
Their party suffered a heavy defeat in the election.

bitter, catastrophic, crushing, devastating, disastrous, embarrassing, humiliating, ignominious (formal)
The battle ended in a humiliating defeat.

narrow
They lost 4–3 in their second narrow defeat of the week.

consecutive, successive
final, ultimate
election, electoral, political
military

accept, admit, concede
She is very determined, and will never admit defeat.
The prime minister conceded defeat and resigned.

face
experience, suffer
go down to, slump to (both BrE,sports)
The team went down to their fifth consecutive defeat.

reverse (BrE)
A good politician can always reverse any defeats.

avoid
We just need to avoid defeat in our last two games.

inflict
The army inflicted a heavy defeat on rebel forces.

end in
lead to

defeat against
last week's crushing defeat against their rivals

defeat by
their defeat by the Brazilians

defeat at the hands of sb
The team suffered defeat at the hands of their oldest rivals.

turn defeat into a victory
They turned a military defeat into a media victory.

comprehensively (BrE), convincingly (esp. BrE), decisively, easily, handily (AmE), heavily (BrE), overwhelmingly, roundly, soundly, thoroughly
The English were decisively defeated by the rebels in the battle that followed.
The senator was decisively defeated by his rivals.

completely, totally
militarily
He said it was impossible to defeat the terrorists militarily.

narrowly
Our team was narrowly defeated in the final.

eventually, finally, ultimately

by
The motion was defeated by 20 votes to 18.

Defeat is used with these nouns as the subject:
army

Defeat is used with these nouns as the object:
amendment, army, bill, challenger, champion, communism, enemy, evil, fleet, foe, initiative, measure, menace, military, monster, motion, opponent, purpose, rebel, regime, rival, terror, terrorism, tyranny