Semi
Part of speech: noun
Definition: A semi-detached house. A semitrailer; a tractor-trailer; an 18 wheeler. A partial erection.
Semifinal
Part of speech: noun
Definition: A playoff in the round with only four players or teams left, the stage before the final.(General) A competition that narrows a field of contestants (semifinalists) to a set of finalists, for a subsequent final.