Ring up mutual fund (4)
I believe the answer is:
loop
'ring' is the definition.
(a loop is a ring of material)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for loop that I've seen before include "Shape formed by a closed curve that does not intersect itself" , "Computer subroutine" , "Endless strip of tape" , "going round" , "Contraception device - hearing aid" .)