What formal anatomical term is used for an elephant's trunk?

The formal anatomical term for an elephant’s trunk is proboscis.

A proboscis is the elephant’s elongated, flexible nose and upper lip, fused into one extraordinary appendage. It is prehensile, meaning the elephant can use it to grasp objects, strip leaves, lift food and draw water into the mouth. It also serves as a sensitive organ for smelling, touching and communicating.

The trunk contains no bones and is powered by dense layers of muscle. It functions as a muscular hydrostat: controlled contractions change its shape and position without a rigid internal skeleton. Elephants use it for delicate tasks, such as picking up a single blade of grass, as well as forceful work, including moving branches or probing soil.

“Proboscis” comes from an ancient Greek word associated with a nose or snout and is also used more broadly in zoology for elongated nose-like structures. An elephant’s trunk is not an antenna, mandible or rostrum. The mandible is the lower jaw, while a rostrum is a projecting snout or beak-like structure in other animals.