As jazzgirl said, it doesn’t fit with the crossing answers. Enough said. They are called crosswords for a reason!
It’s much more common in non-cryptics, eg the clue “put off” being DETER or DEFER, but occasionally is seen in cryptics. Not long ago in the Guardian the clue was: Book, not initially non-fiction (4).
- - T -
An obvious answer was ACTS - [f]acts for the book of the New Testament.
The actual answer was RUTH - [t]ruth for the book of the Old Testament.
Whole crosswords have been constructed around this premise. When done deliberately it is an art, as in Two Grids with One Stone by Twin, in Magpie 235.
Here is another famous one from 1996:
https://www.xwordinfo.com/Crossword?date=11%2F5%2F1996