The crossword solution for the term NATURAL ENDING is IST. IST stands for International Standard Time, which is the standard time zone used by most countries in the world. It is based on the mean solar time at the Royal Observatory in Greenwich, England. IST is used to synchronize clocks around the world and is also known as Greenwich Mean Time or GMT. NATURAL ENDING refers to the fact that IST is the standard time zone used by most countries, providing a NATURAL ENDING point for time zones.