The most common and most likely answer to this crossword clue is the 3 letter word FOG
I've seen this crossword clue in Independent
F
O
G
Buddy explains!

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 FOG mean?
FOG noun- A thick cloud that forms near the ground; the obscurity of such a cloud.
- A mist or film clouding a surface.
- A state of mind characterized by lethargy and confusion.
- A silver deposit or other blur on a negative or developed photographic image.
- Distance fog.
- To become covered with or as if with fog.
- To become obscured in condensation or water.
- To become dim or obscure.
- To make dim or obscure.
- To cover with or as if with fog.
- To disperse insecticide into (a forest canopy) so as to collect organisms.
- To obscure in condensation or water.
- To make confusing or obscure.
- To practice in a small or mean way; to pettifog.
- A new growth of grass appearing on a field that has been mowed or grazed.
- Tall and decaying grass left standing after the cutting or grazing season; foggage.
- Moss.
- To pasture cattle on the fog, or aftergrass, of; to eat off the fog from.
- To become covered with the kind of grass called fog.