The most common and most likely answer to this crossword clue is the 5 letter word COOMB
I've seen this crossword clue in The Guardian
C
O
O
M
B
Buddy explains!

The straight part
We know that "depression" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case depression = coomb.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 COOMB mean?
COOMB noun- An old English measure of corn (e.g., wheat), equal to half a quarter or 4 bushels.
- A valley, often wooded and often with no river
- A cirque.