The most common and most likely answer to this crossword clue is the 11 letter word SUBDIVISION
I've seen this crossword clue in The Guardian
S
U
B
D
I
V
I
S
I
O
N
Buddy explains!

The straight part
We know that "unit/unit" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unit/unit = subdivision.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 SUBDIVISION mean?
SUBDIVISION noun- A division into smaller pieces of something that has already been divided.
- Such a piece that has been divided.
- A parcel of land that has been divided into lots.
- A group of houses created by the same builder or in the same general area.
- A gated community.
- To separate something into smaller pieces.