The term 'little opening' can be summarized by the crossword solution 'nano, ' which is a four-letter word. Nano is derived from the Greek word for 'DWARF' and is used to describe objects that are extremely small in size, typically measuring one billionth of a meter or less. Nano technology is a field of science that focuses on manipulating matter at the atomic and molecular level. It is used in a variety of applications, such as medical treatments, energy production, and environmental protection.