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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 ��ŧ������, meaning “half-unit,” and –que, a suffix meaning “and.” The Greek cognate of ��ŧ������ is ��ŧ����-, meaning “half,” which is the source of terms such as hemisphere. To learn more, check out our 51�Թ�s That Use article on the combining form hemi-.

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-

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?