The marriage union can be cold, in Kew (7)
I believe the answer is:
wedlock
'the marriage' is the definition.
(synonyms)
'union can be cold in kew' is the wordplay.
I cannot really see how this works, but
an anagram of 'cold' is 'dloc' which is present in the answer.
an anagram of 'kew' is 'wek' which is located in the left over letters.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for wedlock that I've seen before include "A state of union" , "State of marriage" , "Marital state" , "Matrimony" , "The married state - throw away the key" .)