The writer’s advisor accepting second idea, initially as a reminder of impermanence (7,4)
I believe the answer is:
memento mori
'reminder of impermanence' is the definition.
'memento mori' can be an answer for 'reminder' (memento mori is a kind of reminder). I am not sure about the 'of impermanence' bit.
'the writer's advisor accepting second idea initially as a' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'second' could be 'mo' (both are short periods of time) and 'mo' is located in the answer.
'writer' could be 'me' (the person who wrote the clues) and 'me' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for memento mori that I've seen before include "A reminder of death's inevitability" , "Reminder that death is inevitable (Latin)" , "Reminder of death (eg, skull) (Lat.)" , "Reminder of expiry" , "skull perhaps" .)