Like simple random number generator, sugar? (5)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

CUBIC – I am defeated by the wordplay or second definition here, as I can’t see how CUBIC can be defined as random.  Surely a cube of a number (a CUBIC ) is clearly defined as the number raised to the power three?  However, see the material in the introduction to the blog that attempts to relate CUBIC to randomness.