The most common and most likely answer to this crossword clue is the 5 letter word MONAD
I've seen this crossword clue in The Guardian
M
O
N
A
D
Buddy explains!
The straight part
We know that "Very keen to keep working for unity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case very keen to keep working for unity = monad.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 MONAD mean?
MONAD noun- An ultimate atom, or simple, unextended point; something ultimate and indivisible.
- A single individual (such as a pollen grain) that is free from others, not united in a group.
- A monoid object in the category of endofunctors of a fixed category.