Jump To:

• semi
  semi

  noun

  semitrailer.
• semi-
  semi-

  a combining form borrowed from Latin, meaning “half,” freely prefixed to English words of any origin, now sometimes with the senses “partially,” “incompletely,” “somewhat”.
• semi–
  semi–

  A prefix that means “half,” (as in semicircle, half a circle) or “partly, somewhat, less than fully,” (as in semiconscious, partly conscious).

semi

¹ American  

[sem-ee, sem-ahy] / ˈsɛm i, ˈsɛm aɪ /

noun

Informal.

• semis
  plural

1. semitrailer.

2. Often semifinal.

---

semi- ² American  

1. a combining form borrowed from Latin, meaning “half,” freely prefixed to English words of any origin, now sometimes with the senses “partially,” “incompletely,” “somewhat”.

   semiautomatic; semidetached; semimonthly; semisophisticated.

---

semi ¹ British  

/ ˈsɛmɪ /

noun

1. a semidetached house

2. short for semifinal

3. short for semitrailer

---

semi- ² British  

prefix

1. half Compare demi- hemi-

   semicircle

2. partially, partly, not completely, or almost

   semiprofessional

   semifinal

3. occurring twice in a specified period of time

   semiannual

   semiweekly

---

semi– Scientific  

1. A prefix that means “half,” (as in semicircle, half a circle) or “partly, somewhat, less than fully,” (as in semiconscious, partly conscious).

---

Usage

What does semi- mean? Semi- is a combining form used like a prefix meaning “half.” In some instances, it is used figuratively to mean "partially," "incompletely," or "somewhat." It is often used in a variety of technical and everyday terms. Semi- comes from Latin sēmi-, meaning “half.” The Greek cognate of sēmi- is hēmi-, also meaning “half,” which is the source of English terms such as hemialgia and hemicardia. To learn more, check out our entries for both words.

Commonly Confused

See bi- ¹.

Other Word Forms

Noun Inflected Forms

• semis
  plural

Etymology

Origin of semi¹

By shortening

Origin of semi-²

Middle English < Latin sēmi-; cognate with Old English sōm-, sām- half (modern dial. sam- ), Old High German sāmi-, Sanskrit sāmi-, Greek hēmi-; cf. sesqui-

Example Sentences

See Examples For:

semi semi- semi– semis

Moderna stock surged following positive cancer-vaccine data, burning short sellers and spilling over into the semi sector.

From Barron's ● Aug. 21, 2026

On an earnings call, Musk walked back earlier guidance on the rollout of its Robotaxi ride-hailing service, Optimus humanoid robots and an electric semi truck that has been in development for years.

From The Wall Street Journal ● Jul. 23, 2026

A spot in the semi finals is on the line.

From BBC ● Jul. 11, 2026

Dashcam video of the incident showed traffic slowing down far ahead of the white Jeep as it stopped abruptly in front of the semi, causing the truck to rear-end the vehicle.

From Los Angeles Times ● Jul. 11, 2026

In theory, bi attached to the front of a word means “two,” and semi means “half” Although Moose says he’s bilingual, he’s semiliterate.

From "Woe Is I" by Patricia T. O'Conner

He “did not adopt a reflexive posture to protect himself and ... he may have fallen in a state of semi- or total unconsciousness,” officials said last month.

From Los Angeles Times ● Nov. 7, 2024

Semi-pedestal sinks are wall-hung sinks with a semi- or half-pedestal attached to the bottom of the sink.

From Seattle Times ● Feb. 28, 2022

Mr Stevenson, who died in 2004, had officiated at the semi- final of the 1979 tournament, and offered to take the child to the final.

From BBC ● Dec. 5, 2016

He's doubled it in a course of almost eight years, seven-and-a-half years, to be semi- exact.

From Washington Post ● Sep. 26, 2016

If there’s no and or but in between, use a semi- colon instead.

From "Woe Is I" by Patricia T. O'Conner

Whole vase covered with thin semi– lustrous wash varying from red–brown to black.

From How to Observe in Archaeology by Various

Powering aboard the 75-foot Mighty Mary, the women defeated the legendary Dennis Conner’s Stars & Stripes in the semis to book a spot in the final.

From The Wall Street Journal ● Oct. 2, 2026

Rangers have only failed to get to the semis once in the past decade.

From BBC ● Sep. 12, 2026

Ben Shelton to the semis 🔥 Shelton outlasts the defending champion Alcaraz in a five-set thriller!

From Los Angeles Times ● Sep. 9, 2026

During the second quarter, traders piled into leveraged products like ETFs to try and cash in on the red-hot rally in semis.

From MarketWatch ● Jul. 28, 2026

Tony and Shawn had left the mountain, but they’d left to do what my father had taught them to do: drive semis, weld, scrap.

From "Educated" by Tara Westover