The most common and most likely answer to this crossword clue is the 6 letter word FROSTY
I've seen this crossword clue in The Daily Telegraph
F
R
O
S
T
Y
More clues leading to the result FROSTY
- Cold tailless amphibian atop animal enclosure
- Forbidding cook to recruit east German
- For altering, place that’s messy and cold
- Unfriendly to opposite pen
- US poet over years lacking enthusiasm
- Actor Stephen receiving East German with hostile demeanour
- Unfriendly father at the front of old hovel
- Unenthusiastic, US poet on fourth of July
- Snowman’s young embraces big teddy’s head
- Fine story to be rewritten? Cool
Buddy explains!

The straight part
We know that "with hostile demeanour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case with hostile demeanour = frosty.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 FROSTY mean?
FROSTY adjective- Cold, chilly.
- Having frost on it.
- Having an aloof or inhospitable manner.