The most common and most likely answer to this crossword clue is the 5 letter word HYDRA
I've seen this crossword clue in The Times
H
Y
D
R
A
More clues leading to the result HYDRA
- Gruesome Hardy monster
- Marine creature in fine fettle, flipping all but head
- Hard nuts cracked by unknown group of stars
- Monster in Binchy drama
- One renewed after cuts put an end to by Labour
- Monstrous serpent appears in filthy drain
- Stars taking part in noteworthy drama
- Monster in filthy drain
- Tips from harpy with a way to upset monster
- Monster in filmography – Dracula
Buddy explains!

The straight part
We know that "group of stars" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case group of stars = hydra.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 HYDRA mean?
HYDRA noun- Any of several small freshwater polyps of the genus Hydra and related genera, having a naked cylindrical body and an oral opening surrounded by tentacles.
- A dragon-like creature with many heads and the ability to regrow them when maimed.
- A complex, multifarious problem or situation that cannot be solved easily and rapidly.