Soldier very nearly became a donor (5)
I believe the answer is:
giver
'a donor' is the definition.
('giver' can be a synonym of 'donor')
'soldier very nearly' is the wordplay.
'soldier' becomes 'gi' (government issue or general issue**).
'nearly' means to remove the last letter.
'very' with its final letter taken off is 'ver'.
'gi'+'ver'='GIVER'
'became' is the link.
(Other definitions for giver that I've seen before include "presenter" , "Present source" , "Donor" , "Bestower" .)