The most common and most likely answer to this crossword clue is the 4 letter word MARE
M
A
R
E
More clues leading to the result MARE
- Horse from Durham area
- Roman sea horse
- Mother concerned with horse
- Horse, ecstasy and smack are on the rise
- Horse and English sheep turned up
- Mother gets about on a horse
- Horseman changes side
- Become aware stuff brought about tense, messy affair
- Horse that can be seen on the moon!
- Materials used to portray pond plant
Buddy explains!

The straight part
We know that "messy affair" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case messy affair = mare.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 MARE mean?
MARE noun- An adult female horse.
- A foolish woman.
- A type of evil spirit formerly thought to sit on the chest of a sleeping person; also, the feeling of suffocation felt during sleep, attributed to such a spirit.
- A demon or monster, thought to plague people while they slept and cause a feeling of suffocation and terror during sleep.
- Sleep paralysis.
- A very bad or frightening dream.
- Any bad, miserable, difficult or terrifying situation or experience that arouses anxiety, terror, agony or great displeasure.
- A large, dark plain, which may have the appearance of a sea.
- On Saturn's moon Titan, a large expanse of what is thought to be liquid hydrocarbons.