Element

Atomic weight: Variable

Properties: entirely dependent on the story requirements of whichever science illiterate hack has been commissioned to write this week's episode of your favourite science fiction show.

Related to Unobtanium. The principle difference being that Unobtanium is usually the maguffin that drives the plot whilst Plotonium resolves the corner the writer wrote themselves into.
Dilithium is the magical material that drives warp drives in Star Trek and, despite the series having strong science advisors on hand, writers still tested in-story credibility to breaking point.

"The Plotonium fuel rods have overheated and disrupted the flow of Unobtanium to the Maguffin drive....we're all doomed!"
by Apocrypha September 29, 2013
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