The most common and most likely answer to this crossword clue is the 4 letter word LOSS
I've seen this crossword clue in Independent
L
O
S
S
More clues leading to the result LOSS
- Cost of polish, not good
- Disadvantage the Spanish suffered originally
- Fatality in plant — bug not involved
- Defeat left horses missing odd bits
- Casualty cast sacrificing time for rehearsal at last
- See ship dropping
- Behold saints making sacrifice?
- Speculate to accumulate with such a do seller’s organised
- Big band leader‘s bereavement
- Deficit in accounts solicitor raised
Buddy explains!

The straight part
We know that "Defeat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case defeat = loss.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LOSS mean?
LOSS noun- The result of no longer possessing an object, a function, or a characteristic due to external causes or misplacement.
- The destruction or ruin of an object.
- Something that has been destroyed or ruined.
- Defeat; an instance of being defeated.
- The death of a person or animal.
- The condition of grief caused by losing someone or something, especially someone who has died.
- (financial) The sum an entity loses on balance.
- Electricity of kinetic power expended without doing useful work.