The crossword solution for the term 'PREFIX WITH 'FRIENDLY' OR 'TOURISM'' is ECO, which is a three-letter prefix. ECO is derived from the Greek word oikos, meaning 'HOUSE' or 'HOME'. It is commonly used to refer to environmentalism and ecology, as well as economic and social issues related to sustainability. ECO is often used as a prefix for words such as 'ecofriendly' and 'ecotourism', which refer to practices that are environmentally friendly and sustainable.