The most common and most likely answer to this crossword clue is the 10 letter word FRATERNISE
I've seen this crossword clue in Financial Times
F
R
A
T
E
R
N
I
S
E
More clues leading to the result FRATERNISE
- Winger breaking Cantona’s strawberry hobnob
- Bird in fine breed for associate
- Associate with retainers thrown out by force
- Mix fluid after rinse
- Make friends with bird eating French fruit? On the contrary
- Female faces fee increase, accommodating new consort
- Consort with fellow and bird in lift
- Consort with female and grow embracing bird
- Mix finest rare ingredients
- Consort’s potty, after rinse
Buddy explains!

The straight part
We know that "Associate with" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case associate with = fraternise.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 FRATERNISE mean?
FRATERNISE verb- To associate with others in a brotherly or friendly manner.
- To associate as friends with an enemy, in violation of duty.
- To have an intimate or sexual relationship with a forbidden member of the opposite sex; as, in some cases, football players with cheerleaders.