The Collaborative International Dictionary
astrochemistry \astrochemistry\ n. the branch of science involving astronomy and chemistry which studies the chemical composition, chemical reactions, and evolution of matter in outer space. -- as`tro*chem"ic*al, a. -- as`tro*chem"ic*al*ly, adv.
Wiktionary
n. (context chemistry astronomy English) The study of the chemical composition of stars and outer space
Wikipedia
Astrochemistry is the study of the abundance and reactions of chemical elements and molecules in the universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium. The study of the abundance of elements and isotope ratios in Solar System objects, such as meteorites, is also called cosmochemistry, while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form.