Does anyone know an elegant synonym for the "mixer" portion of a cocktail?

Maybe go French (that always makes things more elegant, don't you agree?): le mixer. ;)

Often these are called modifiers -- they can be anything from citrus juice, to aperitifs, to syrups to sodas. Our cocktail columnist Erik talks a little bit about them here: http://food52.com/blog/10100-when-to-shake-or-stir-a-cocktail