Stable sustenance (4)
I believe the answer is:
oats
'stable sustenance' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oats that I've seen before include "Wild ones are sown in youthful excess" , "Porridge mix" , "Edible grass seeds" , "Porridge ingredient" , "Grains used as food and fodder" .)