The most common and most likely answer to this crossword clue is the 10 letter word NATURALISE
I've seen this crossword clue in Independent
N
A
T
U
R
A
L
I
S
E
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 NATURALISE mean?
NATURALISE verb- To grant citizenship to someone not born a citizen
- To acclimatize an animal or plant
- To make natural
- To limit explanations of a phenomenon to naturalistic ones and exclude supernatural ones
- To make (a word) a natural part of the language.
- To study nature.