Real Dictionary

steroid
a chemical substance produced in an endocrine gland and transported in the blood to a certain tissue, on which it exerts a specific effect [...]
any of a large group of fat-soluble organic compounds containing a characteristic chemical ring system. The majority, including the sterols, bile acids, many hormones, and the D vitamins, have important physiological action [...]
countable noun: A steroid is a type of chemical substance found in your body. Steroids can be artificially introduced into the bodies of athletes to improve their strength.