noun.
a foodadditive that sweetens, especially an artificialsubstitute for sugar
noun.
something added as an inducement or incentive; a kickback
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
something added to foods to make them taste sweeter
noun.
anything that serves as an enticement
Word Usage
"The sweetener is that the first 500 people to book tickets using their Twitter ID would be able to redeem a 50% discount (still valid as of 2pm EDT, 20 Feb)."