The most common and most likely answer to this crossword clue is the 9 letter word SOCIALISE
I've seen this crossword clue in The Times
S
O
C
I
A
L
I
S
E
Buddy explains!
The straight part
We know that "Mix" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mix = socialise.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 SOCIALISE mean?
SOCIALISE verb- To interact with others
- To instruct somebody, usually subconsciously, in the etiquette of a society
- To take something into collective or governmental ownership