Give money to Caruso, say, but not O. Henry (6)
I believe the answer is:
enrich
'give money to' is the definition.
(to make rich)
'caruso say but not o henry' is the wordplay.
'caruso say' becomes 'Enrico' (opera singer Enrico Caruso, 1873-1921).
'but not' is a deletion indicator.
'henry' becomes 'H' (symbol for the unit of electrical inductance).
'enrico' with 'o' removed is 'enric'.
'enric'+'h'='ENRICH'
(Other definitions for enrich that I've seen before include "increase wealth" , "Grace" , "Make fuller flavoured" , "Add nutrients to" , "Improve, soil say" .)