Semi

Semi is a prefix derived from the Latin semi-, meaning "half" or "partly." It forms adjectives and nouns to indicate partialness, incompleteness, or duality. Its usage spans everyday language, science, mathematics, and technology.

In everyday language, semi describes something not complete or only partly true: semi-final, semi-annual, semi-truck, semi-detached house. The spelling and punctuation of semi compounds vary by style and context; some forms are hyphenated, others are closed or open compounds.

In science and mathematics, semi- appears in terms such as semimetal, semiconductor, semigroup, semiring, and semifield. In statistics and related fields, semi-parametric models blend parametric and nonparametric elements. The prefix helps denote entities that behave like half or partial versions of their full counterparts.

In transportation, semi commonly refers to a semi-trailer and the tractor unit that pulls it. A semi-truck pulls a semi-trailer that carries its own load and attaches via a fifth wheel, and the term is widely used in North American trucking to distinguish it from full trailers.

SEMI is also the acronym for Semiconductor Equipment and Materials International, a global industry association that develops standards, best practices, and events for the microelectronics supply chain.

Etymology and usage notes: semi derives from Latin, and its form may be hyphenated or closed in compounds; its meaning can shift from literal “half” to “partly” or “somewhat” depending on context.