The word "内分泌" is formed by combining the characters 内 (nèi), meaning "inside" or "internal", 分 (fēn), meaning "to divide" or "to secrete", and 泌 (mì), meaning "to secrete" or "to excrete", together creating the concept of "internal secretion", which in medical context refers to the endocrine system where glands secrete hormones directly into the bloodstream.