semi /semee/ , /semi:/ 1. n. Abbreviation for semicolon , when speaking. Commands to grind are prefixed by semi-semi-star means that the prefix is ;;* , not 1/4 of a star. 2. A prefix used with words such as immediately as a qualifier. When is the system coming up? Semi-immediately. (That is, maybe not for an hour.) We did consider that possibility semi-seriously. See also infinite.