The most common and most likely answer to this crossword clue is the 3 letter word ECO
I've seen this crossword clue in The Daily Telegraph
E
C
O
More clues leading to the result ECO
- Italian writer represented by English firm
- Writer excising chapter one first of all
- Green, yet crop is to be cut, oddly
- Business established by end of village green
- Such people like collecting bottles?
- Green author
- Late genius that may prefix other solutions
- Local bee could provide notice of environmental impact
- Trips escort arranged around Oxford University
- Voyager going green in choppy cruise to welcoming shores of Tobago
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 ECO mean?
ECO adjective- Environmentally friendly or sensitive.
- A proposed name for the common currency that the West African Monetary Zone plans to introduce in the framework of the Economic Community of West African States.