A substitute's place (5)
I believe the answer is:
stead
'a substitute's place' is the definition.
'stead' can be an answer for 'place' (synonyms). I'm unsure of the 'a substitute's' bit.
'a substitute's place' is the wordplay.
I cannot really understand how this works, but
'a' is present in the answer.
'place' could be 'sted' (I have seen 'Old place' mean 'sted' so perhaps 'place' could also mean 'sted') and 'sted' is located in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for stead that I've seen is " Place, function or role of another".)