The most common and most likely answer to this crossword clue is the 4 letter word JUNK
I've seen this crossword clue in The Guardian
J
U
N
K
More clues leading to the result JUNK
Buddy explains!
The straight part
We know that "Horse/which is valueless" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case horse/which is valueless = junk.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 JUNK mean?
JUNK noun- Discarded or waste material; rubbish, trash.
- A collection of miscellaneous items of little value.
- Any narcotic drug, especially heroin.
- The genitalia.
- Salt beef.
- Pieces of old cable or cordage, used for making gaskets, mats, swabs, etc., and when picked to pieces, forming oakum for filling the seams of ships.
- A fragment of any solid substance; a thick piece; a chunk.
- Material or resources of a kind lacking commercial value.
- To throw away.
- To find something for very little money (meaning derived from the term junk shop)
- A Chinese sailing vessel.