In this union, we had to keep things safe (7)
I believe the answer is:
wedlock
'in this union' is the definition.
'wedlock' can be an answer for 'union' (synonyms). I'm not certain of the remainder of the definition.
'we had to keep things safe' is the wordplay.
I cannot quite understand how this works, but
'we' is found in the answer.
'had' could be 'd' (I've seen this in other clues) and 'd' is found within the answer.
The remaining letters 'lock' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for wedlock that I've seen before include "A state of union" , "Marital state" , "Matrimony" , "The married state - throw away the key" , "State of marriage" .)