1. Wall, often battered, also called a revetment, preventing a bank of earth, etc., from slipping: it is found in the form of battered arched piers at the back of which are segmental concave walls (like vaults) to resist the pressure behind them, often associated with C19 railway architecture.
2. A dam.
"retaining-wall." A Dictionary of Architecture and Landscape Architecture. . Encyclopedia.com. (October 19, 2018). http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/retaining-wall
"retaining-wall." A Dictionary of Architecture and Landscape Architecture. . Retrieved October 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/education/dictionaries-thesauruses-pictures-and-press-releases/retaining-wall