The most common and most likely answer to this crossword clue is the 4 letter word ZEBU
I've seen this crossword clue in The Daily Telegraph
Z
E
B
U
Buddy explains!
The straight part
We know that "Ox" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ox = zebu.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 ZEBU mean?
ZEBU noun- A domesticated ox native to Asia and Africa, having a large fleshy hump on its back and a dewlap (Bos primigenius indicus).