Merriam-Webster Collegiate Dictionary - between

 I. preposition  Etymology: Middle English betwene, preposition & adverb, from Old English betweonum, from be- + -tweonum (dative plural) (akin to Gothic tweihnai two each); akin to Old English twa two  Date: before 12th century  1.  a. by the common action of ; jointly engaging shared the work ~ the two of them talks ~ the three — Time  b. in common to ; shared by divided ~ his four grandchildren  2.  a. in the time, space, or interval that separates  b. in intermediate relation to  3.  a. from one to another of air service ~ Miami and Chicago  b. serving to connect or unite in a relationship (as difference, likeness, or proportion) a one-to-one correspondence ~ sets  c. setting apart the line ~ fact and fancy  4.  a. in preference for one or the other of had no difficulty deciding ~ the two  b. in point of comparison of not much to choose ~ the two coats  5. in confidence restricted to a secret ~ you and me  6. taking together the combined effect of ~ work and family life, they have no time for hobbies Usage:  There is a persistent but unfounded notion that ~ can be used only of two items and that among must be used for more than two. Between has been used of more than two since Old English; it is especially appropriate to denote a one-to-one relationship, regardless of the number of items. It can be used when the number is unspecified economic cooperation ~ nations, when more than two are enumerated ~ you and me and the lamppost partitioned ~ Austria, Prussia, and Russia — Nathaniel Benchley, and even when only one item is mentioned (but repetition is implied) pausing ~ every sentence to rap the floor — George Eliot. Among is more appropriate where the emphasis is on distribution rather than individual relationships discontent among the peasants. When among is automatically chosen for more than two, English idiom may be strained a worthy book that nevertheless falls among many stools — John Simon the author alternates among mod slang, cliches and quotes from literary giants — A. H. Johnston.  II. adverb  Date: before 12th century in an intermediate space or interval