The most common and most likely answer to this crossword clue is the 4 letter word SOIL
I've seen this crossword clue in The Daily Telegraph
S
O
I
L
More clues leading to the result SOIL
- Dirty farm building, with nothing moved inside
- Start to scrub grease stain
- Dirty pictures finish on top
- Earth, one going round sun? Just the opposite
- Manure ground
- Edge of dress getting grease and grime
- It’s foul being this poorly without the end in sight
- Dirty, therefore I left
- Dirty son with something greasy
- I put in ‘Sun’ — correct answer is ‘Earth’
Buddy explains!

The straight part
We know that "Dirty" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dirty = soil.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 SOIL mean?
SOIL noun- A mixture of mineral particles and organic material, used to support plant growth.
- The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
- The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.
- Country or territory.
- That which soils or pollutes; a stain.
- A marshy or miry place to which a hunted boar resorts for refuge; hence, a wet place, stream, or tract of water, sought for by other game, as deer.
- Dung; compost; manure.
- Faeces or urine etc. when found on clothes.
- A bag containing soiled items.
- To make dirty.
- To become dirty or soiled.
- To stain or mar, as with infamy or disgrace; to tarnish; to sully.
- To dirty one's clothing by accidentally defecating while clothed.
- To make invalid, to ruin.
- To enrich with soil or muck; to manure.
- A wet or marshy place in which a boar or other such game seeks refuge when hunted.
- To feed, as cattle or horses, in the barn or an enclosure, with fresh grass or green food cut for them, instead of sending them out to pasture; hence (such food having the effect of purging them), to purge by feeding on green food.