The most common and most likely answer to this crossword clue is the 7 letter word CASHIER
I've seen this crossword clue in The Daily Telegraph
C
A
S
H
I
E
R
More clues leading to the result CASHIER
- Fire bank employee
- Dismiss person handling money
- Dismiss bank clerk
- Dismiss bank employee
- Drum out tosser, roughly at first
- Charlie, a comparatively mousy employee in bank
- Disgracefully dismiss money: that is, rupees
- Sack race unexpectedly disrupted by his blundering
- Dishonourably discharge bank employee
- Sack finance department employee
Buddy explains!

The straight part
We know that "Sack" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sack = cashier.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 CASHIER mean?
CASHIER verb- To dismiss (someone, especially military personnel) from service
- To discard, put away
- To annul
- One who works at a till or receives payments.
- Person in charge of the cash of a business or bank.