Hemi-sphere is a word derived from the Greek root words, 'hemi', which means half, and 'sphere', which means a round object. As such, it pertains to one half of a spherical object such as the earth. Some synonyms for the word hemisphere include half-sphere, semisphere, and demi-sphere. Other words that pertain to the concept of a half-object include demilune, which refers to the shape of a half-moon, and hemicycle, which pertains to a circular or semicircular structure. In science, hemisphere is synonymous with the term 'lobes' as in the brain lobes, which are divided into two hemispheres- the left and the right.