The most common and most likely answer to this crossword clue is the 6 letter word SHARED
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More clues leading to the result SHARED
Buddy explains!

The straight part
We know that "joint" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case joint = shared.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 SHARED mean?
SHARED verb- To give part of what one has to somebody else to use or consume.
- To have or use in common.
- To divide and distribute.
- To tell to another.
- To cut; to shear; to cleave; to divide.
- Used by multiple entities or for multiple purposes or in multiple ways.