Is it ensure, insure, or assure?
"an equal half," mid-15c., from Old French moite, earlier meitiet (12c., Modern French moitié) "half; middle; portion, piece," from Latin meditatem (nominative medietas) "half," originally "middle point," from medius "middle" (see medial (adj.)).
moiety moi·e·ty (moi'ĭ-tē)
One of two or more parts into which something may be divided, such as the various parts of a vitamin or molecule.