The most common and most likely answer to this crossword clue is the 4 letter word BOIL
I've seen this crossword clue in The Guardian
B
O
I
L
More clues leading to the result BOIL
Buddy explains!
The straight part
We know that "to turn into vapour" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to turn into vapour = boil.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 BOIL mean?
BOIL noun- A localized accumulation of pus in the skin, resulting from infection.
- The point at which fluid begins to change to a vapour.
- A dish of boiled food, especially based on seafood.
- The collective noun for a group of hawks.
- (of liquids) To heat to the point where it begins to turn into a gas.
- To cook in boiling water.
- (of liquids) To begin to turn into a gas, seethe.
- To bring to a boil, to heat so as to cause the contents to boil.
- (used only in progressive tenses, of weather) To be uncomfortably hot.
- (used only in progressive tenses) To feel uncomfortably hot.
- To form, or separate, by boiling or evaporation.
- To steep or soak in warm water.
- To be agitated like boiling water; to bubble; to effervesce.
- To be moved or excited with passion; to be hot or fervid.