The most common and most likely answer to this crossword clue is the 9 letter word RETENTION
I've seen this crossword clue in The Daily Telegraph
R
E
T
E
N
T
I
O
N
More clues leading to the result RETENTION
- Keeping daughter out of school punishment after resistance
- Keeping school punishment with new head taking over
- Revise rent, I note, or enter into continued possession
- Keeping on temporary accomÂmodation
- Keeping hospital department in Orient running
- Enter into arrangement for holding on to staff
- Soldiers with stress reported ability to remember
- Being disturbed, enter into custody
- Memory of number in Orient being tortured
- Keeping school punishment right for a day
Buddy explains!

The straight part
We know that "custody" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case custody = retention.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 RETENTION mean?
RETENTION noun- The act of retaining or something retained
- The act or power of remembering things
- A memory; what is retained in the mind
- The involuntary withholding of urine and faeces
- The length of time an individual remains in treatment
- That which contains something, as a tablet; a means of preserving impressions.
- The act of withholding; restraint; reserve.
- A place of custody or confinement.
- The right to withhold a debt, or of retaining property until a debt due to the person claiming the right is duly paid; a lien.