Unconventional Irish soldier? (9)
I believe the answer is:
irregular
'unconventional' is the definition.
('irregular' can be similar in meaning to 'unconventional')
'irish soldier?' is the wordplay.
'irish' becomes 'ir' (abbreviation).
'soldier?' becomes 'regular' (member of the regular army).
'ir'+'regular'='IRREGULAR'
(Other definitions for irregular that I've seen before include "somewhat odd" , "Lacking continuity or contrary to the rule" , "commonest verbs?" , "unlike full-time soldiers" , "Disorderly, uneven" .)