Undertake to reduce? (8)
I believe the answer is:
contract
I believe this is a double definition.
'undertake' is the first definition.
(I know that undertake can be written as contract)
'to reduce?' is the second definition.
(I know that contract is a kind of reduce)
(Other definitions for contract that I've seen before include "Shrink from the business agreement" , "Shrink in legal agreement?" , "Agreement - lessen" , "Shrink in written agreement" , "Binding agreement between two or more" .)