The most common and most likely answer to this crossword clue is the 8 letter word ASTERISM
A
S
T
E
R
I
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M
Buddy explains!
The straight part
We know that "For instance, Hydra" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case for instance, hydra = asterism.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 ASTERISM mean?
ASTERISM noun- (constellation) An unofficial constellation (small group of stars that forms a visible pattern).
- A rarely used typographical symbol (⁂, three asterisks arranged in a triangle), used to call attention to a passage or to separate subchapters in a book.
- A star-shaped figure exhibited by some crystals by reflected light (as in a star sapphire) or by transmitted light (as in some mica).