Longman Dictionary of Contemporary English
The Collaborative International Dictionary
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
(assimilated as dif- before -f-, to di- before most voiced consonants), word-forming element meaning
"lack of, not" (as in dishonest);
"do the opposite of" (as in disallow);
"apart, away" (as in discard), from Old French des- or directly from Latin dis- "apart, in a different direction, between," figuratively "not, un-," also "exceedingly, utterly," from PIE *dis- "apart, asunder" (cognates: Old English te-, Old Saxon ti-, Old High German ze-, German zer-).\n
\nThe PIE root is a secondary form of *dwis- and thus is related to Latin bis "twice" (originally *dvis) and to duo, on notion of "two ways, in twain."\n
\nIn classical Latin, dis- paralelled de- and had much the same meaning, but in Late Latin dis- came to be the favored form and this passed into Old French as des-, the form used for new compound words formed in Old French, where it increasingly had a privative sense ("not").\n
\nIn English, many of these words eventually were altered back to dis-, while in French many have been altered back to de-. The usual confusion prevails.
pre. 1 reversal or removal 2 apart 3 (non-gloss definition: Used as an intensifier of words with negative valence.)