Determined soldier must support a parent (7)
I believe the answer is:
adamant
'determined' is the definition.
(I've seen this before)
'soldier must support a parent' is the wordplay.
'soldier' becomes 'ant' (I've seen this before).
'must support' says to put letters next to each other (I've seen this in other clues).
'a parent' becomes 'adam' (biblical parent).
'ant' after 'adam' is 'ADAMANT'.
(Other definitions for adamant that I've seen before include "Resolute, refusing to yield" , "Obdurate and unyielding" , "unshakeable in purpose" , "Refusing to change one's mind" , "Resolute; diamond (arch.)" .)