somnambulism (n.)youdaoicibaDictYouDict[somnambulism 词源字典]
1786, "walking in one's sleep or under hypnosis," from French somnambulisme, from Modern Latin somnambulus "sleepwalker," from Latin somnus "sleep" (see Somnus) + ambulare "to walk" (see amble (v.)).

Originally brought into use during the excitement over "animal magnetism;" it won out over noctambulation. A stack of related words came into use early 19c., such as somnambule "sleepwalker" (1837, from French somnambule, 1690s), earlier somnambulator (1803); as adjectives, somnambulary (1827), somnambular (1820). [somnambulism etymology, somnambulism origin, 英语词源]
noctambulistyoudaoicibaDictYouDict
"A sleepwalker", Mid 18th century: from Latin nox, noct- 'night' + ambulare 'to walk' + -ist.
noctambulationyoudaoicibaDictYouDict
"Sleepwalking", Early 18th century: from Latin nox, noct- 'night' + ambulatio(n-) (from ambulare 'to walk').