What does "tug" mean?

Additional senses

1. 2.To pull with great effort; to strain in labor; as, to tug at the oar; to tug against the stream. He tugged, he shook, till down they came. Milton.
2. 3.To labor; to strive; to struggle. England now is left To tug and scamble and to part by the teeth The unowed interest of proud-swelling state. Shak.
3. 4.A pull with the utmost effort, as in the athletic contest called tug of war; a supreme effort. At the tug he falls, Vast ruins come along, rent from the smoking walls. Dryden.
4. 5.A sort of vehicle, used for conveying timber and heavy articles. [Prov. Eng.] Halliwell.
5. 6.(Naut.) A small, powerful steamboat used to tow vessels; -- called also steam tug, tugboat, and towboat.
6. 7.A trace, or drawing strap, of a harness.
7. 8.(Mining.) An iron hook of a hoisting tub, to which a tackle is affixed. Tug iron, an iron hook or button to which a tug or trace may be attached, as on the shaft of a wagon.