The most common and most likely answer to this crossword clue is the 6 letter word STARVE
I've seen this crossword clue in The Guardian
S
T
A
R
V
E
More clues leading to the result STARVE
- Something rude to do is eating very fast
- Staff without rupees suffer from hunger
- Two ways to overcome resistance fast
- Look to eat little volume and go very hungry
- Look to pen verse fast?
- Staff maintaining right to deprive of food
- Some superstar vegans have nothing to eat
- Avert accident after bend that’s fast
- Go without saying “tara”, and regret virtually everything, first of all
- Look meaningfully round very fast
Buddy explains!

The straight part
We know that "fast" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fast = starve.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 STARVE mean?
STARVE verb- To die; in later use especially to die slowly, waste away.
- To die because of lack of food or of not eating.
- To be very hungry.
- To destroy, make capitulate or at least make suffer by deprivation, notably of food.
- To deprive of nourishment or of some vital component.
- To deteriorate for want of any essential thing.
- (especially Yorkshire and Lancashire) To kill with cold.