The most common and most likely answer to this crossword clue is the 5 letter word TURBO
I've seen this crossword clue in The Guardian
T
U
R
B
O
Buddy explains!

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 TURBO mean?
TURBO noun- Turbocharger.
- Turbojet.
- Turbomolecular pump.
- Autofire.
- To autofire.
- With rapidly-increasing blind levels.
- Causing or relating to increased speed.
- A turban shell.