The most common and most likely answer to this crossword clue is the 4 letter word REEF
I've seen this crossword clue in The Guardian
R
E
E
F
More clues leading to the result REEF
- Bar charging nothing, beginning to end
- Bank charge brought back after resistance
- At first really envious, eying fine part of sail
- Knot, turnstone etc may feed here
- Bank charge right to go up
- Admire efforts to circumvent danger to shipping?
- Bank‘s not entirely free finance
- Ridge in portion of sail
- & 2dn. Loopy thing madly keen to take top of fork in balls
- Bank customer’s last payment is returned
Buddy explains!

The straight part
We know that "Bank" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bank = reef.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 REEF mean?
REEF noun- A chain or range of rocks, sand, or coral lying at or near the surface of the water.
- A large vein of auriferous quartz; hence, any body of rock yielding valuable ore.
- A portion of a sail rolled and tied down to lessen the area exposed in a high wind.
- A reef knot.
- To take in part of a sail in order to adapt the size of the sail to the force of the wind.
- To pull or yank strongly, especially in relation to horse riding.
- (of paddles) To move the floats of a paddle wheel toward its center so that they will not dip so deeply.
- The itch; any eruptive skin disorder.
- Dandruff.
- Scabby; scurvy.