The prefix semi- means “half” or “partially.” In general it combines with adjectives: semiattached, semidry, semisweet.Semi- also combines, less commonly, with nouns: semidarkness, semidesert, semidome. Semi- can be compared with the prefixes hemi- and demi-. All three have basically the same meaning, but semi- comes from Latin semi-, meaning “half,” and hemi- comes from Greek hemi-, meaning “half.” Demi- comes from Latin dimidius, meaning “divided in half,” from dis, “apart, asunder” plus medius, “half.”
