The most common and most likely answer to this crossword clue is the 10 letter word MATTERHORN
I've seen this crossword clue in The Guardian
M
A
T
T
E
R
H
O
R
N
More clues leading to the result MATTERHORN
- Mountain concern — something sounding warning?
- Mountain, terrible threat in early part of day
- Concern linked to side of Himalayan mountain
- Steep mountain presenting dire threat in early part of day
- Mountain stuff, something hard
- Before noon, possibly, completely lowering milliner’s cap’s peak
- Instrument blown after affair’s high point
- The thing that blows on a mountain
Buddy explains!
The straight part
We know that "Steep mountain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case steep mountain = matterhorn.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.