Reproduce, proliferate (8)
I believe the answer is:
multiply
I believe this is a double definition.
'reproduce' is the first definition.
(I know that multiply is a more specific form of the action reproduce)
'proliferate' is the second definition.
(I know that proliferate is a more specific form of the action multiply)
(Other definitions for multiply that I've seen before include "Increase the number" , "in several ways, each with its own stress" , "Add one number to itself" , "Increase, procreate" , "Add an amount to itself a number of times" .)