The most common and most likely answer to this crossword clue is the 4 letter word ILIA
I've seen this crossword clue in The Guardian
I
L
I
A
Buddy explains!

The straight part
We know that "bones" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bones = ilia.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 ILIA mean?
ILIA noun- The upper and widest of the three bones that make up each side of the hipbone and pelvis.
- The ileum, part of the small intestine.