Substantial string of properties (4)
I believe the answer is:
rope
'substantial string' is the definition.
'rope' can be an answer for 'string' (I have seen 'string of pearls' mean 'rope' so perhaps 'string' could also mean 'rope'). I'm unsure of the 'substantial' bit.
'of properties' is the wordplay.
'of' indicates a hidden word.
'ROPE' is hidden in the letters of 'properties'.
(Other definitions for rope that I've seen before include "Pore over a woven cord" , "Maybe tied up in bonds" , "A thick strong cord" , "Give a man enough . . . . and he'll hang himself" , "Guy" .)