The most common and most likely answer to this crossword clue is the 4 letter word CHUM
I've seen this crossword clue in The Daily Telegraph
C
H
U
M
More clues leading to the result CHUM
- Friend initially creates unpleasant smell
- Friend immersed in public humiliation
- Friend quietly abandons idiot
- Buddy and Charlie don’t know the words?
- China much misrepresented
- Buzz following check, initially, and mate
- Blockhead losing pawn, leading to mate
- Foolish person falling short as a friend
- Copper’s intertwined with royal associate
- Bud is of almost easily duped sort
Buddy explains!

The straight part
We know that "mate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mate = chum.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 CHUM mean?
CHUM noun- A friend; a pal.
- A roommate, especially in a college or university.
- To share rooms with someone; to live together.
- To lodge (somebody) with another person or people.
- To make friends; to socialize.
- To accompany.
- A mixture of (frequently rancid) fish parts and blood, dumped into the water to attract predator fish, such as sharks
- To cast chum into the water to attract fish.
- A coarse mould for holding the clay while being worked on a whirler, lathe or manually.