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a combining form meaning “one and a half,” used in the formation of compound words: sesquicentennial.
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Origin of sesqui-

<Latin sēsqui-<*sēm(i)sque, equivalent to sēmis half-unit, semis + -que and (cognate with Greek té,Sanskrit ca,Gothic -uh)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does sesqui- mean?

Sesqui– is a combining form used like a prefix meaning “one and a half.” It is occasionally used in scientific terms, especially in chemistry.

Sesqui– comes from Latin and is equivalent to sēmis, meaning “half-unit,” and –que, a suffix meaning “and.” The Greek cognate of sēmis is hēmi-, meaning “half,” which is the source of terms such as hemisphere. To learn more, check out our Words That Use article on the combining form hemi-.

Examples of sesqui-

One example of a technical term that uses sesqui– is sesquicentennial, “pertaining to or marking the completion of a period of 150 years.”

The sesqui– part of the word means “one and a half,” as we know. The word centennial may also seem familiar; it means “pertaining to a period of 100 years.” Sesquicentennial literally translates to “pertaining to a period of 150 years.”

What are some words that use the combining form sesqui-?

What are some other forms that sesqui– may be commonly confused with?

Break it down!

Sesquipedalian means “given to using long words.” The suffix –pedalian means roughly “measuring a foot.” Given the meaning of sesqui-, what does sesquipedalian literally translate to?

How to use sesqui- in a sentence

  • At length it was discovered that sesqui-sulphide of phosphorus would make just as good matches and was harmless.

    Makers of Many Things|Eva March Tappan
  • We may, for example, differentiate in this way the alkaline bicarbonates from the sesqui-carbonates or the carbonates.

    The Mechanism of Life|Stphane Leduc
  • Float the paper on a solution of the sesqui-chloride of iron.

  • Sesqui-, Latin for one and a half; so Sesquipedalis, a foot and a half long.

British Dictionary definitions for sesqui-


indicating one and a halfsesquicentennial
(in a chemical compound) indicating a ratio of two to threesesquioxide

Word Origin for sesqui-

from Latin, contraction of semi- + as as ² + -que and
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012