any person who advocates or works to protect the air, water, animals, plants, and other natural resources from pollution or its effects.
3.
a person who believes that differences between individuals or groups, especially in moral and intellectual attributes, are predominantly determined by environmental factors, as surroundings, upbringing, or experience (opposed to hereditarian).
British Dictionary definitions for environmentalism
environmentalism
/ɪnˌvaɪrənˈmɛntəˌlɪzəm/
noun
1.
(psychol) the belief that a person's behaviour is affected chiefly by his environment Compare hereditarianism
environmentalist
/ɪnˌvaɪrənˈmɛntəlɪst/
noun
1.
an adherent of environmentalism
2.
a person who is concerned with the maintenance of ecological balance and the conservation of the environment
3.
a person concerned with issues that affect the environment, such as pollution
Word Origin and History for environmentalism
n.
1923, as a psychological theory (in the nature vs. nurture debate), from environmental + -ism. The ecological sense is from 1972. Related: Environmentalist (n.), 1916 in the psychological sense, 1970 in the ecological sense.