The most common and most likely answer to this crossword clue is the 6 letter word SUTURE
I've seen this crossword clue in The Times
S
U
T
U
R
E
More clues leading to the result SUTURE
- Joining group of workers engaged by firm
- Certain trade union’s covered medical procedure
- Stitch uterus after an operation
- Girl involves most of cast in stitch up
- Treatment of wound succeeded — tomorrow sees female heading off
- Stitch up trade union in firm
- Repair damaged uterus
- It joins in operations
- Surgical treatment certain to restrict two regular members of United
- Stitch operated uterus
Buddy explains!

The straight part
We know that "Joining" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case joining = suture.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 SUTURE mean?
SUTURE noun- A seam formed by sewing two edges together, especially to join pieces of skin in surgically treating a wound.
- Thread used to sew or stitch two edges (especially of skin) together.
- An area where separate terrane join together along a major fault.
- A type of fibrous joint bound together by Sharpey's fibres which only occurs in the skull.
- A seam or line, such as that between the segments of a crustacean, between the whorls of a univalve shell, or where the elytra of a beetle meet.
- The seam at the union of two margins in a plant.
- To sew up or join by means of a suture.