Support South American volunteers at home (7)
I believe the answer is:
sustain
'support' is the definition.
('sustain' can be a synonym of 'support')
'south american volunteers at home' is the wordplay.
'south american' becomes 'sus' (I've seen this in other clues).
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'sus'+'ta'+'in'='SUSTAIN'
(Other definitions for sustain that I've seen before include "Nurture, uphold" , "Keep up; hold for a long time" , "Prolong, support" , "Keep (something) going" , "Strengthen, support" .)