Semi-opalescent is a descriptive term used to describe something that is partially translucent and partially opaque. It is often used to describe a material or substance that has some reflective properties, but is not completely transparent. Synonyms for semi-opalescent could include iridescent, pearlescent, shimmering, opaline, translucent, semi-transparent, and translucently opaque. These words can all be used to describe the same characteristic of a material or substance. Depending on the context in which the word is used, different synonyms may be more appropriate. However, all these words convey a sense of partial transparency or reflectiveness.