The crossword solution for the term TWO-THIRDS OF SESQUI- is UNI, which stands for 'UNITARY'. UNITARY is an adjective that describes something that is composed of one part or element. This term is often used in mathematics and physics to describe a system that is composed of a single entity. In this case, TWO-THIRDS OF SESQUI- is referring to a UNITARY system that is composed of two-thirds of a sesqui- (a prefix meaning 'one and a half').