"Mamenchisaurus" means 'Mamenchi lizard', from the Chinese Pinyin "mǎ" (马 'horse') and "mén" (门 'gate'), while "chi" is a transliteration of "xī" (溪 'stream' or 'brook'), combined with the suffix "-saurus" (from Greek "sauros" meaning 'lizard'). The intention was to name the genus after the place where its fossil was first found. However, due to an accentual mix-up by Young, the location name "Mǎmíngxī" (马鸣溪 'horse-neighing brook') was mistaken as "Mǎménxī" (马门溪 'horse-gate brook'). The fact that the first "Mamenchisaurus" fossil was found due to construction work led to Young's naming the type species as "Mamenchisaurus constructus".