The most common and most likely answer to this crossword clue is the 12 letter word INHOSPITABLE
I've seen this crossword clue in Financial Times
I
N
H
O
S
P
I
T
A
B
L
E
Buddy explains!
The straight part
We know that "unfriendly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unfriendly = inhospitable.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 INHOSPITABLE mean?
INHOSPITABLE adjective- (of a person) Not inclined to hospitality; unfriendly,
- (of a place) Not offering shelter; barren or forbidding.