In general, a proboscis (from Greek προ, pro "before" and βοσκειν, boskein "to feed")'s an elongated appendage from the head of an animal, either a vertebrate or an invertebrate.. Etymology The correct Greek plural's proboscides, but in English it's more common to simply add -es, forming proboscises. Although the word derives from the Greek "pro-boskein", the Latin spelling "proboscis"'s taken in favor of the Greek "proboskis". Invertebrates T… (More on Proboscis)