Etymology
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somnambulism (n.)
1786, "walking in one's sleep or under hypnosis," from French somnambulisme, from Modern Latin somnambulus "sleepwalker," from Latin somnus "sleep" (from PIE root *swep- "to sleep") + 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).
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somnambulate (v.)
1821, probably a back-formation from somnambulism, from French somnambulisme, from Modern Latin somnambulus "sleepwalker," from Latin somnus "sleep" (from PIE root *swep- "to sleep") + ambulare "to walk" (see amble (v.)). Related: Somnambulated; somnambulating.
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*ambhi- 
also *mbhi-, Proto-Indo-European root meaning "around;" probably derived from *ant-bhi "from both sides," from root *ant- "front, forehead."

It forms all or part of: abaft; about; alley (n.1) "open passage between buildings;" ambagious; ambassador; ambi-; ambidexterity; ambidextrous; ambience; ambient; ambiguous; ambit; ambition; ambitious; amble; ambulance; ambulant; ambulate; ambulation; ambulatory; amphi-; amphibian; Amphictyonic; amphisbaena; Amphiscians; amphitheater; amphora; amputate; amputation; ancillary; andante; anfractuous; be-; begin; beleaguer; between; bivouac; but; by; circumambulate; embassy; ember-days; funambulist; ombudsman; perambulate; perambulation; preamble; somnambulate; somnambulism; umlaut.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit abhitah "on both sides," abhi "toward, to;" Avestan aibi; Greek amphi "round about;" Latin ambi- "around, round about;" Gaulish ambi-, Old Irish imb- "round about, about;" Old Church Slavonic oba; Lithuanian abu "both;" Old English ymbe, German um "around."
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mesmerism (n.)

"the doctrine that one person can exercise influence over the will and nervous system of another and produce certain phenomena by virtue of a supposed emanation called animal magnetism," 1798, from French mesmérisme, named for Franz Anton Mesmer (1734-1815), Austrian physician who developed a theory of animal magnetism and a mysterious body fluid which allows one person to hypnotize another and propounded it in 1778 in Paris. The word, if still used is practically synonymous with hypnotism or artificial somnambulism. Another similar word for the same effect was braidism. An old term for "hypnotic suggestion" was mesmeric promise. Related: Mesmerist

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