1.  between(r = adv.all) betwixt - in the interval; "dancing all the dances with little rest between"

2.  between(r = adv.all) 'tween - in between; "two houses with a tree between"

1.  In the space which separates; betwixt; as, New York is between Boston and Philadelphia. [1913 Webster]

2.  Used in expressing motion from one body or place to another; from one to another of two. [1913 Webster]
"If things should go so between them." [1913 Webster]

3.  Belonging in common to two; shared by both. [1913 Webster]
"Castor and Pollux with only one soul between them." [1913 Webster]

4.  Belonging to, or participated in by, two, and involving reciprocal action or affecting their mutual relation; as, opposition between science and religion. [1913 Webster]
"An intestine struggle, open or secret, between authority and liberty." [1913 Webster]

5.  With relation to two, as involved in an act or attribute of which another is the agent or subject; as, to judge between or to choose between courses; to distinguish between you and me; to mediate between nations. [1913 Webster]

6.  In intermediate relation to, in respect to time, quantity, or degree; as, between nine and ten o'clock. [1913 Webster]
"I . . . hope that between public business, improving studies, and domestic pleasures, neither melancholy nor caprice will find any place for entrance." [1913 Webster]

   Intermediate time or space; interval. Shak. [1913 Webster]

between, prep. & adv.
--prep.
1 a at or to a point in the area or interval bounded by two or more other points in space, time, etc. (broke down between London and Dover; we must meet between now and Friday). b along the extent of such an area or interval (there are five shops between here and the main road; works best between five and six; the numbers between 10 and 20).
2 separating, physically or conceptually (the distance between here and Leeds; the difference between right and wrong).
3 a by combining the resources of (great potential between them; between us we could afford it). b shared by; as the joint resources of ({pound}5 between them). c by joint or reciprocal action (an agreement between us; sorted it out between themselves).

Idiom:
between ourselves (or you and me) in confidence. between times (or whiles) in the intervals between other actions; occasionally.

Usage:
In sense 3 with reference to more than two people or things is established and acceptable (e.g. relations between Britain, France, and Germany).
4 to and from (runs between London and Sheffield).
5 taking one and rejecting the other of (decide between eating here and going out).
--adv. (also in between) at a point or in the area bounded by two or more other points in space, time, sequence, etc. (not fat or thin but in between).

Etymology:
OE betweonum f. Gmc (as BY, TWO)

N  interposition, interjacence, intercurrence, intervenience, interlocation, interdigitation, interjection, interpolation, interlineation, interspersion, intercalation, interpenetration, permeation, infiltration, intervention, interference, intrusion, obtrusion, insinuation, insertion, dovetailing, embolism, intermediary, intermedium, go between, bodkin, intruder, interloper, parenthesis, episode, flyleaf, partition, septum, diaphragm, midriff, dissepiment, party wall, panel, room divider, halfway house, interjacent, intercurrent, intervenient, intervening, intermediate, intermediary, intercalary, interstitial, embolismal, parenthetical, episodic, mediterranean, intrusive, embosomed, merged, between, betwixt, twixt, among, amongst, amid, amidst, mid, midst, in the thick of, betwixt and between, sandwich-wise, parenthetically, obiter dictum.

between decks, between the lines, betwixt and between, come between, go between, read between the lines, war between the states