The most common and most likely answer to this crossword clue is the 10 letter word PALATINATE
I've seen this crossword clue in The Guardian
P
A
L
A
T
I
N
A
T
E
Buddy explains!
The straight part
We know that "Territory" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case territory = palatinate.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 PALATINATE mean?
PALATINATE noun- The office or rank of a palatine.
- A territory ruled by a palatine.
- A native or inhabitant of such a territory.
- Of or pertaining to a palatinate or the Palatinate.