The most common and most likely answer to this crossword clue is the 4 letter word VOID
I've seen this crossword clue in The Times
V
O
I
D
More clues leading to the result VOID
Buddy explains!

The straight part
We know that "empty space" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case empty space = void.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 VOID mean?
VOID noun- An empty space; a vacuum.
- An extended region of space containing no galaxies
- A collection of adjacent vacancies inside a crystal lattice.
- A pocket of vapour inside a fluid flow, created by cavitation.
- An empty space between floors or walls, including false separations and planned gaps between a building and its facade.
- To make invalid or worthless.
- To empty.
- To throw or send out; to evacuate; to emit; to discharge.
- To withdraw, depart.
- To remove the contents of; to make or leave vacant or empty; to quit; to leave.
- Containing nothing; empty; not occupied or filled.
- Having no incumbent; unoccupied; said of offices etc.
- Being without; destitute; devoid.
- Not producing any effect; ineffectual; vain.
- Of no legal force or effect, incapable of confirmation or ratification.
- Containing no immaterial quality; destitute of mind or soul.
- (of a function or method) That does not return a value.
- A voidee.