Crossword Genius

Marriage in trade group (5)

Ross

I believe the answer is:

union

I'm a little stuck... Click here to teach me more about this clue!

'marriage' is the definition.
(I know that marriage can be written as union)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for union that I've seen before include "Coalescence, join as one" , "workers' co-operative" , "Big old pearl" , "The joining of two or more together" , "Climbing plant" .)

I've seen this clue in The Mirror.
Want a hint initially instead of a full solution? Install my app