noun /'delt'
1. the fourth letter of the Greek alphabet ( ð D 2. a word used in communications to represent the letter D 3. (math) an incremental change in a variable 4. (chem) the amount of energy [expressed in joules] that is needed to convert all the molecules in on mole of a reacting substance from a ground state to a transition state. 5. a quantative change
noun /'nIgm'
1. a riddle; a statement, picture or question etc. the hidden meaning of which is to be discovered. 2. a puzzle 3. something hard to understand or explain 4. an inscrutable or mysterious person. 5. An electric rotor cipher machine, invented in the 1920's, that was used to generate codes for the Germans during World War II.