n 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  :  HEADACHE  3  :  a projection or extremity esp. of an anatomical part: as  a  :  the rounded proximal end of a long bone (as the humerus)  b  :  the end of a muscle nearest the origin  c  :  the anterior end of an invertebrate  :  SCOLEX  4  :  the part of a boil, pimple, or abscess at which it is likely to break  5  :  the end of a lipid molecule that consists of a polar group and is regarded as being opposite to the tail head adj 
 
 
 
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