1. The division of the human body that contains the brain, the eyes, the ears, the nose, and the mouth; also: the corresponding anterior division of the body of various animals including all vertebrates, most arthropods, and many mollusks and worms. 2. A projection or extremity especially of an anatomical part. 3. The rounded proximal end of a long bone (as the humerus). 4. The end of a muscle nearest the origin. 5. The anterior end of an invertebrate. 6. The part of a boil, pimple, or abscess at which it is likely to break. 7. The end of a lipid molecule that consists of a polar group and is regarded as being opposite to the tail.