The most common and most likely answer to this crossword clue is the 4 letter word SUCK
I've seen this crossword clue in The Times
S
U
C
K
Buddy explains!
The straight part
We know that "creation of partial vacuum" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case creation of partial vacuum = suck.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 SUCK mean?
SUCK noun- An instance of drawing something into one's mouth by inhaling.
- Milk drawn from the breast.
- A weak, self-pitying person; a person who refuses to go along with others, especially out of spite; a crybaby or sore loser.
- A sycophant, especially a child.
- A short drink, especially a dram of spirits.
- An act of fellatio.
- To use the mouth and lips to pull in (a liquid, especially milk from the breast).
- To perform such an action; to feed from a breast or teat.
- To put the mouth or lips to (a breast, a mother etc.) to draw in milk.
- To extract, draw in (a substance) from or out of something.
- To work the lips and tongue on (an object) to extract moisture or nourishment; to absorb (something) in the mouth.
- To pull (something) in a given direction, especially without direct contact.
- To perform fellatio.
- To be inferior or objectionable: a general term of disparagement, sometimes used with at to indicate a particular area of deficiency.