The most common and most likely answer to this crossword clue is the 6 letter word SNATCH
I've seen this crossword clue in The Sunday Telegraph
S
N
A
T
C
H
Buddy explains!
The straight part
We know that "Fraction of a number" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fraction of a number = snatch.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 SNATCH mean?
SNATCH noun- A quick grab or catch.
- A competitive weightlifting event in which a barbell is lifted from the platform to locked arms overhead in a smooth continuous movement.
- A piece of some sound, usually music or conversation.
- The vulva.
- A brief period of exertion.
- A catching of the voice.
- A hasty snack; a bite to eat.
- A quibble.
- To grasp and remove quickly.
- To attempt to seize something suddenly.
- To take or seize hastily, abruptly, or without permission or ceremony.
- To steal.
- (by extension) To take (a victory) at the last moment.
- To do something quickly in the limited time available.