The most common and most likely answer to this crossword clue is the 4 letter word DIKE
D
I
K
E
More clues leading to the result DIKE
Buddy explains!

The straight part
We know that "dam" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dam = dike.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 DIKE mean?
DIKE verb- Alternative form of dyke: to dig a ditch; to raise an earthwork; etc.
- (usually derogatory) A lesbian, particularly one with masculine or butch traits or behavior.
- A well-dressed man.
- Formalwear or other fashionable dress.
- To be well dressed.
- (usually derogatory) A lesbian, particularly one with masculine or butch traits or behavior.