After onset of stress, mean to slacken off (4,4)
I believe the answer is:
slow down
'slacken off' is the definition.
'slow down' can be an answer for 'slacken' (synonyms). I am not sure about the 'off' bit.
'after onset of stress mean' is the wordplay.
'after' says to put letters next to each other.
'onset of' indicates taking the first letters.
'mean' becomes 'lowdown' (I've seen this before).
The initial letter of 'stress' is 's'.
's'+'lowdown' is 'SLOW-DOWN'.
'to' is the link.
Can you help me to learn more?
(Other definitions for slow down that I've seen before include "Don't go so fast" , "relax" , "take it more easy" , "Reduce speed" , "Lose velocity" .)