The word "subfemtosecond" refers to a unit of time that is smaller than one quadrillionth of a second. While this term is highly specific, there are other ways to describe incredibly short intervals of time. Some synonyms for "subfemtosecond" include "attosecond," "zeptosecond," and "yoctosecond." These terms describe intervals of time that are even smaller than a femtosecond. They are often used in the study of atomic and molecular physics, where extremely short pulses of laser light are used to observe and manipulate the behavior of individual atoms and molecules. Understanding these tiny time scales is critical for advancing our knowledge of the fundamental properties of matter.