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
Out of all the responses so far ...... by Brian Smith)
Perhaps geographic/linguistic region plays a part here, but I've never heard of a "quag." I don't doubt everyone, I've just never heard this particular term. Then again I wouldn't have immediately recognized "oleo" either. Taxicab is a slam dunk as far as I can see...