The most common and most likely answer to this crossword clue is the 6 letter word OREADS
I've seen this crossword clue in The Daily Telegraph
O
R
E
A
D
S
More clues leading to the result OREADS
Buddy explains!

The straight part
We know that "Nymphs" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nymphs = oreads.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 OREADS mean?
OREADS noun- A mountain nymph; an anthropomorphic appearance of the spirit of a mountain.