The most common and most likely answer to this crossword clue is the 8 letter word MATCHING
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result MATCHING
Buddy explains!
The straight part
We know that "Joining in marriage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case joining in marriage = matching.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 MATCHING mean?
MATCHING verb- To agree; to be equal; to correspond.
- To agree with; to be equal to; to correspond to.
- To make a successful match or pairing.
- To equal or exceed in achievement.
- To unite in marriage, to mate.
- To fit together, or make suitable for fitting together; specifically, to furnish with a tongue and groove at the edges.
- The process by which things are matched together or paired up.
- A set of independent edges in a given graph, i.e. a set of edges which do not intersect, such that pairs of vertices are "matched" to each other one to one.
- The same as another; sharing the same design.