One for union to travel on bike at first (5)
I believe the answer is:
bride
'one for union' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'travel on bike at first' is the wordplay.
'travel' becomes 'ride' (eg to ride a bus).
'on' says to put letters next to each other.
'at first' says to take the initial letters.
The first letter of 'bike' is 'b'.
'ride' put after 'b' is 'BRIDE'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for bride that I've seen before include "presumably honeymoon for me?" , "The Woman In White, perhaps?" , "She's just about to be married" , "Woman getting wed" , "Wife of groom" .)