The most common and most likely answer to this crossword clue is the 7 letter word SPECTRE
I've seen this crossword clue in The Times
S
P
E
C
T
R
E
More clues leading to the result SPECTRE
- Ghost creeps eerily round back of apartment
- Dreadful secret involving quiet ghost
- Seeing first couple last, admire ghost
- Spirit of staff having mushroom turnover
- Relation’s about to go over to the other side in haunting image
- In retrospect, realise it’s a ghost
- Villainous group terribly secret seizing power
- Evil organisation quietly residing in secret complex
- Respect changes an unpleasant image
- Respect lively spirit
Buddy explains!

The straight part
We know that "ghost" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ghost = spectre.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 SPECTRE mean?
SPECTRE noun- A ghostly apparition, a phantom.
- A threatening mental image.