Environmental chemistry studies the chemical processes that shape ecosystems and determine the quality of air, water, and soil. It examines how natural cycles maintain balance, how pollutants disrupt these systems, and how chemistry can be applied to protect and restore the environment. By exploring interactions between chemicals and the natural world, this field helps explain issues such as acid rain, heavy metal contamination, and nutrient cycles. Placed within the broader discipline of chemistry, environmental study links fundamental reactions to real-world challenges. It connects laboratory insights with global concerns like climate change, waste management, and sustainable resource use. Understanding the chemical nature of these problems equips learners and professionals with the knowledge to contribute to solutions that affect both society and the planet. This dictionary organizes the essential terms of environmental chemistry into concise yet comprehensive entries. Topics range from atmospheric pollutants and soil chemistry to water treatment and toxicology. Each entry is written with context that supports students, guides educators, and provides clarity for specialists working across environmental sciences and applied chemistry. Using a dictionary as a learning tool strengthens familiarity with the language of science and makes it easier to connect ideas across disciplines. For readers at any stage of study, such structured references provide lasting educational value. Mastery of environmental chemistry terminology not only supports academic progress but also fosters informed participation in one of the most pressing areas of modern science.