A hard metallic alloy that was invented in the late 1980's by musical pop-star Adam Ant.

It is often melted down and applied as a type of hair mousse amongst image conscious musicians to produce a "big hair" look that is not only functional but is also completely resistant to moisture, heat, radiation, acid, hurricane force winds and small arms fire.
Hey Rogue, how do you get your hair to do that?

I put adamantium in it.
by NephilimNexus March 8, 2009
An unrealistic plot device, utilised in a film to tie up any loose ends that a stupid and/or confusing script happens to offer to the viewer.
See Wolverine Origins.

Stryker:'This adamantium bullet should tie up any plot holes!'
by Matt_Owen May 19, 2009