Aapekshikam= relative... a thing having a relation to or connection with or necessary dependence on another thing.

Because in many situations the gravitational field doesn't show any dependence on time (excluding some situations of oscillating fields) it satisfies requirements for a system to be conservative (in order a system to be conservative it's potential energy should not have dependence on time).

Yes dependence is the base word for co-dependence.

Dependence that is not physiologically based.

Functions are relations where the codomain is dependent on the domain, but relations don't necessarily have this dependence. By the way, there is no formal proof distinguishing these two terms, they can pretty much be used interchangeably.