The most common and most likely answer to this crossword clue is the 5 letter word SERAC
I've seen this crossword clue in The Times
S
E
R
A
C
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The straight part
We know that "icy pinnacle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case icy pinnacle = serac.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 SERAC mean?
SERAC noun- Often sérac: a hard, cone-shaped, pale green, strongly flavoured cheese from Switzerland made from skimmed cowmilk and blue fenugreek (Trigonella caerulea); Schabziger, Sapsago. It is usually eaten grated, mixed with butter, or in a fondue.
- (glaciology) A sharp tower of ice formed by intersecting crevasses of a glacier.