Fall off and Narrow down

Fall off verb - To turn away from a straight line or course.

Narrow down and fall off are semantically related In some cases you can use "Narrow down" instead a verb "Fall off".

Narrow down verb - To reduce in size or volume by or as if by pressing parts or members together.

Fall off and narrow down are semantically related in decrease topic. Sometimes you can use "Fall off" instead a verb "Narrow down", if it concerns topics such as grow less or make less.