- dianeticsA self-help system designed by L. Ron Hubbard, today chiefly employed in Scientology.
- diacodiumA type of syrup made from poppies.
- diapenteThe interval of the fifth or the harmonic ratio 3:2.
- diaphemetricRelating to the measurement of tactile sensibility.
- diatessaronThe interval of a fourth or the harmonic ratio 4:3.