Top Definition
Geek term: A girl who is near-impossible to sleep with. See also frigid.

From an old Star Trek episode. Spock had just analyzed a ship, and said to the captain "Sir, the hull is comprised of pure neutronium, there are no known means of penetration."
I took Lisa out last night, but that girl is pure neutronium.
by rootyb June 01, 2005
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