FOSSIL is an acronym for 'Fossil Fuels and Organic Substances in the Lithosphere'. It refers to the REMAINS of plants, animals, and other organisms that have been preserved in the Earth's crust over millions of years. REMAINS, which is seven letters long, is a term used to describe the physical evidence of these organisms, such as bones, shells, and teeth. OLD, which is three letters long, is a term used to describe something that has existed for a long time. AGED, which is four letters long, is a term used to describe something that has been around for a long period of time. ANCIENT, which is seven letters long, is a term used to describe something that is very OLD, usually thousands of years OLD. Foggy, which is four letters long, is a term used to describe something that is unclear or hard to understand. RELIC, which is five letters long, is a term used to describe something that is very OLD and has survived from a past era. DINOSAUR, which is eight letters long, is a term used to describe a species of extinct reptile that lived during the Mesozoic Era.