The most common and most likely answer to this crossword clue is the 9 letter word ECONOMIST
I've seen this crossword clue in The Guardian
E
C
O
N
O
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T
More clues leading to the result ECONOMIST
- Green film about operating organ
- Environmental refusal supported by film magazine
- Mixed emotions about Conservative finance expert
- Green train is not heading for Milton Keynes?
- Varoufakis, for one, misusing emoticons
- Dismal scientist: “Dynamite to incomes!”
- Taking care of monies, could be expert ultimately?
- Dismal scientist comes in to undergo review
- Hayek, say, giving English company clear conditions
- Notices plastered across front of office opening in Milton Keynes?
Buddy explains!

The straight part
We know that "Keynes?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case keynes? = economist.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 ECONOMIST mean?
ECONOMIST noun- An expert in economics, especially one who studies economic data and extracts higher-level information or proposes theories.
- One concerned with political economy.
- One who manages a household.
- One who economizes, or manages domestic or other concerns with frugality; one who expends money, time, or labor, judiciously, and without waste.