both refer to movie chains (i.e., Loews, AMC Theatres) with movie theatres that screen more than one film at a time, as opposed to single-screen theatres. A multiplex has from 2 up to 16 screens, a megaplex has 16 or more screens; plex is the abbreviation for a multiplex theatre.
A morula (Latin, morus: mulberry) is an early stage embryo consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida.
morpheme (plural morphemes) (linguistic morphology) A smallest linguistic unit within a word that can carry a meaning, such as un-, break, and -able in the word unbreakable. The word pigs consists of two morphemes: pig (a particular animal) and s (indication of the plural).