a combining form meaning “one and a half,” used in the formation of compound words: sesquicentennial.
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. 2019
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
word-forming element, from Latin sesqui- "one-half more," contraction of *semis-que- "a half in addition," from semis "a half" (see semi-) + -que "and," from PIE *kwe-.
Online Etymology Dictionary, © 2010 Douglas Harper