Whittle down
Definition 1 of 2
Pro Tip 1/3Gradual Process
Involves slowly decreasing in stages, not all at once. 
We need to whittle down our expenses over the next few months.
Pro Tip 2/3Narrowing Choices
Used when selecting the best options from many by eliminating others. 
After reviewing all applications, we whittled down the candidates to a select few.
Pro Tip 3/3Strategic Reduction
Implies a thoughtful, deliberate approach to reduction. 
The team worked to whittle down the number of potential project risks.