The term defined as the measure of force gravity acting on the mass of a substance is weight.

Here's why:

* Weight is a force, specifically the force exerted on an object due to gravity.

* Mass is a measure of the amount of matter in an object.

* The relationship between weight and mass is that weight is directly proportional to mass. The stronger the gravitational pull, the heavier the object will feel.

So, if you measure the force of gravity acting on a substance, you are measuring its weight.