The most common and most likely answer to this crossword clue is the 4 letter word BERM
B
E
R
M
More clues leading to the result BERM
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 = berm.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 BERM mean?
BERM noun- A narrow ledge or shelf, as along the top or bottom of a slope
- A raised bank or path, especially the bank of a canal opposite the towpath
- A terrace formed by wave action along a beach
- A mound or bank of earth, used especially as a barrier or to provide insulation
- A ledge between the parapet and the moat in a fortification
- (Indiana) A strip of land between a street and sidewalk
- To provide something with a berm