sesqui-

1. a combining form meaning “one and a half,” used in the formation of compound words:

   sesquicentennial.

sesqui-

prefix

1. indicating one and a half

   sesquicentennial

2. (in a chemical compound) indicating a ratio of two to three

   sesquioxide

Word History and Origins

Origin of sesqui-¹

< Latin sēsqui- < *sēm ( i ) sque, equivalent to sēmis half-unit, semis + -que and (cognate with Greek té, Sanskrit ca, Gothic -uh )

Word History and Origins

Origin of sesqui-¹

from Latin, contraction of semi- + as as ² + -que and

Example Sentences

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

From Project Gutenberg

We may, for example, differentiate in this way the alkaline bicarbonates from the sesqui-carbonates or the carbonates.

From Project Gutenberg

Float the paper on a solution of the sesqui-chloride of iron.

From Project Gutenberg

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

From Project Gutenberg

Words That Use sesqui-

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-?

• sesquialtera
• sesquicarbonate
• sesquihydrate
• sesquioxide
• sesquipedalian (using the equivalent form of sesqui– in Latin)
• sesquiplane

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

• -esque
• septi-
• septo-

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?