Etymology: Believed to be of Australian origin, describing a grunt of exertion, or perhaps a modification of "heave".

Transitive verb: "to hiff (something)":
1. To throw (something) in a cumbersome manner, often something heavy or uncooperative.
2. To dispose of something, often something that has exceeded its usefulness.

Rarely used intransitively, such as in "Dave hiffs".

It is a sound that means nothing at all. Or it is another word for nothing!