A word used in place of crap, shit, or any other words which usually mean bad.
It supposedly originates from the fact that when a word is ~ish (The man was tall....ish. His skin was yellowish in colour, for example), its only partially the full meaning of the word its used with. Tall being taller than
tallish, and yellow being more yellow than yellowish.
Therefore rubbish, without
the ish, would be
rubb. Rubbness of the highest magnitude if you will.