The most common and most likely answer to this crossword clue is the 4 plus 3 letter word THIN AIR
I've seen this crossword clue in The Guardian
T
H
I
N
A
I
R
More clues leading to the result THIN AIR
- Feature of high peak, perhaps, into which one may vanish
- Hit rain, travelling: disappeared into it?
- Nothing found in scrawny Cockney’s coat
- Cryptic hint on vent into which one disappears (4,3
- Feature of an Everest ascent, in which one may disappear
- Into which mountain climbers may disappear?
- Might one disappear into it at the top of Everest?
- Might an East End trichologist treat this for nothing?
- Balding husband disappearing into a state of invisibility?
- Poor Melody, where d’you disappear to?
Buddy explains!
The straight part
We know that "into which one disappears" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case into which one disappears = thin air.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.