opsono-, opson-, opso-; opsino-; opsoni; -opsony +
(Greek: boiled meat; to buy food; to purchase provisions; shopping)
"Something to accompany bread to make it more palatable"; hence, "condiment, relish". Also used with the biochemical suffix -in which is used in naming antibiotics, the idea being that opsonin acts as a "condiment" to make bacteria more "palatable" to phagocytes.