sesqui-

American  

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

   sesquicentennial.

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sesqui- British  

prefix

1. indicating one and a half

   sesquicentennial

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

   sesquioxide

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Usage

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-.

Etymology

Origin of sesqui-

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