sesqui-

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

prefix

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

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-.