Soften the impact of vacuous actions taken by Students' Union over time (7)
I believe the answer is:
assuage
'soften the impact' is the definition.
'assuage' can be an answer for 'soften' (I've seen this in another clue). I am not certain of the 'the impact' bit.
'vacuous actions taken by students' union over time' is the wordplay.
'vacuous' suggests removing the centre.
'taken by students' union over' becomes 'su' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'time' becomes 'age' (an age is a period of time).
'actions' with its middle taken out is 'as'.
'as'+'su'+'age'='ASSUAGE'
'of' is the link.
Can you help me to learn more?
(Other definitions for assuage that I've seen before include "'Make less severe, pain say (7)'" , "Make less intense; satisfy" , "Reduce severity" , "Make less severe, pain or hunger, say" , "Ease or relieve, say thirst" .)