Condiment: from L. condimentum "spice, seasoning, sauce," from condire "to preserve, pickle, season" (variant of condere "to put away, store"). As its etymology suggests, a condiment must have a shelf life -- which, until recently, means it was vinegar-, salt-, or sugar-based. Also, it must be at least slightly more complicated, and moister, than a seasoning.
However, though preserved, pickles aren't condiments: pickled beets can be lovely with falafel, but they're still a vegetable. As for the "usage" folks, who define anything added to prepared food as a condiment, they're quite mad: even if you dip fish sticks into it, hollandaise is a sauce, not a condiment.
