The most common and most likely answer to this crossword clue is the 3 letter word NIB
I've seen this crossword clue in The Times
N
I
B
Buddy explains!

The straight part
We know that "Writer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case writer = nib.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 NIB mean?
NIB noun- The tip of a pen or tool that touches the surface, transferring ink to paper.
- The bill or beak of a bird; the neb.
- Bits of trapped dust or other foreign material that form imperfections in painted or varnished surfaces.
- A piece of a roasted, hulled cocoa bean.
- A small and pointed thing or part; a point; a prong.
- One of the handles projecting from a scythe snath.
- The shaft of a wagon.
- To fit (a pen) with a nib.