Oleomargarine is what margarine was originally called, sometimes shortened to 'oleo'. This makes it one of a select few: words which can be broken into two words, so that each of the two and the original word are synonymous. That is:
oleomargarine = oleo = margarine.
Can you find another two English words that share this property?
(In reply to puzzle solution
by K Sengupta)
downfallen = down = fallen
lowdown = low = down