Delivers one a flower (7)
I believe the answer is:
freesia
'flower' is the definition.
(I've seen this before)
'delivers one a' is the wordplay.
'delivers' becomes 'frees' (both can mean to rescue).
'one' becomes 'i' (roman numeral).
'frees'+'i'+'a'='FREESIA'
(Other definitions for freesia that I've seen before include "bloomer" , "Is the sea rife with these strange flowers?" , "Sea rife with these odd flowers" , "Highly scented flower" , "Fragrant-flowered plant; faeries (anag.)" .)