Support available in First Empire (4)
I believe the answer is:
stem
'support' is the definition.
(I've seen this before)
'available in first empire' is the wordplay.
'available in' says the answer is hidden in the clue.
'STEM' is hidden in the letters of 'first empire'.
(Other definitions for stem that I've seen before include "supporter of tobacco?" , "something growing?" , "root" , "Ski turn and plant stalk" , "Slender upright part, of flower or glass" .)