The most common and most likely answer to this crossword clue is the 7 letter word COPPERS
I've seen this crossword clue in The Guardian
C
O
P
P
E
R
S
More clues leading to the result COPPERS
Buddy explains!
The straight part
We know that "They nick/money" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they nick/money = coppers.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 COPPERS mean?
COPPERS noun- A reddish-brown, malleable, ductile metallic element with high electrical and thermal conductivity, symbol Cu, and atomic number 29.
- The reddish-brown colour/color of copper.
- Any of various specialized items that are made of copper, where the use of copper is either traditional or vital to the function of the item.
- Any of various lycaenid butterflies with copper-coloured upperwings, especially those of the genera Lycaena and Paralucia.
- (law enforcement) A police officer.