The Collaborative International Dictionary
Deuto- \Deu"to-\or Deut- \Deut-\ (d[=u]t-)[Contr. from Gr. dey`teros second.] (Chem.) A prefix which formerly properly indicated the second in a regular series of compound in the series, and not to its composition, but which is now generally employed in the same sense as bi- or di-, although little used.
Dia- \Di"a-\, Di- \Di-\ . [Gr. dia` through; orig., dividing into two parts; akin to ? two. See Two, and cf. 1st Di-.] A prefix denoting through; also, between, apart, asunder, across. Before a vowel dia- becomes di-; as, diactinic; dielectric, etc.
dis- \dis-\ (?; 258)
A prefix from the Latin, whence F. d['e]s, or sometimes d['e]-, dis-. The Latin dis-appears as di-before b, d, g, l, m, n, r, v, becomes dif-before f, and either dis-or di- before j. It is from the same root as bis twice, and duo, E. two. See Two, and cf. Bi-, Di-, Dia-. Dis- denotes separation, a parting from, as in distribute, disconnect; hence it often has the force of a privative and negative, as in disarm, disoblige, disagree. Also intensive, as in dissever.
Note: Walker's rule of pronouncing this prefix is, that the s ought always to be pronounced like z, when the next syllable is accented and begins with ``a flat mute [b, d, v, g, z], a liquid [l, m, n, r], or a vowel; as, disable, disease, disorder, disuse, disband, disdain, disgrace, disvalue, disjoin, dislike, dislodge, dismay, dismember, dismiss, dismount, disnatured, disrank, disrelish, disrobe.'' Dr. Webster's example in disapproving of Walker's rule and pronouncing dis-as diz in only one (disease) of the above words, is followed by recent ortho["e]pists. See Disable, Disgrace, and the other words, beginning with dis-, in this Dictionary.
A prefix from Gr. di`s- twice. See Di-. [1913 Webster] ||
Douglas Harper's Etymology Dictionary
word-forming element meaning "two, double, twice," from Greek di-, from dis "twice," related to duo (see two).
word-forming element meaning "apart, asunder," form of dis- before certain voiced consonants.
word-forming element meaning "through; thoroughly," form of dia- before vowels.
Etymology 1 pre. 1 Meaning two, twice(,) or double. 2 An occasionally used form of dis-. Etymology 2
pre. A form of dia- before a vowel.