fourth letter of the Roman alphabet, from Greek delta, from Phoenician and Hebrew daleth, pausal form of deleth "door," so called from its shape. The form of the modern letter is the Greek delta (Δ) with one angle rounded. As the sign for "500" in Roman numerals, it is said to be half of CIƆ, which was an early form of M, the sign for "1,000." 3-D for "three-dimensional" is attested from 1952.

abstract suffix of state, from Old English dom "statute, judgment" (see doom (n.)). Originally an independent word, but already active as a suffix in Old English (as in freodom, wisdom). Cognate with German -tum (Old High German tuom). "Jurisdiction," hence "province, state, condition, quality."

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

in the metric system, word-forming element denoting one-tenth of the standard unit of measure, 1801, from French deci-, taken arbitrarily from Latin decimus "tenth," from decem "ten" (from PIE root *dekm- "ten").

word-forming element meaning "half, half-sized, partial," used in English from mid-14c., especially in technical terms from French, from Old French demi "half" (12c.), from Late Latin dimedius, from Latin dimidius "half, one-half," which contains the elements dis- "apart" (see dis-) + medius "in the middle, between; from the middle," as a noun "the middle;" from PIE root *medhyo- "middle." Formerly also demy-, and in early use often written as a separate word.

word-forming element meaning "tree," from Greek dendron "tree," sometimes especially "fruit tree" (as opposed to hylē "timber"), from PIE *der-drew-, from root *deru- "to be firm, solid, steadfast," also forming words for "wood, tree."

also desoxy-, word-forming element used to make chemical names for compounds which contain fewer oxygen atoms than other compounds, from de- + first two syllables of oxygen.

word-forming element meaning "of or pertaining to skin," from Greek dermat-, from derma "(flayed) skin, leather," from PIE root *der- "to split, flay, peel," with derivatives referring to skin and leather. The shortened form derm- was used from mid-19c. but is considered incorrect.