The most common and most likely answer to this crossword clue is the 9 letter word EVAPORATE
E
V
A
P
O
R
A
T
E
More clues leading to the result EVAPORATE
- Put back flag, make speech and vanish
- Put down flags, turning to speak, and vanish
- Give address on back cover and melt away
- Prepare ground for upcoming harangue and vanish
- Give address on back cover, otherwise disappear
- Tape over bum hiding one’s boil away
- Quietly speak in support of Argentinian lady and disappear
- Dry lecture follows hoisting of flag
- Create surface cover, set up and talk at length; vanish
- Make speech after returning flag and disappear
Buddy explains!

The straight part
We know that "vanish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vanish = evaporate.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 EVAPORATE mean?
EVAPORATE verb- To transition from a liquid state into a gaseous state
- To expel moisture from (usually by means of artificial heat), leaving the solid portion
- To give vent to; to dissipate
- To disappear; to escape or pass off without effect