Dictionary.com
definitions

decrement

[dek-ruh-muh nt]
noun
  1. the act or process of decreasing; gradual reduction.
  2. the amount lost by reduction.
  3. Mathematics. a negative increment.
  4. Physics. the ratio of amplitudes of a damped harmonic motion in the course of two successive oscillations.

Origin of decrement

1475–85; < Latin dēcrēmentum, equivalent to dēcrē(tus) (see decrease) + -mentum -ment
Related formsdec·re·men·tal [dek-ruh-men-tl] /ˌdɛk rəˈmɛn tl/, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for decremental

decrement

noun
  1. the act of decreasing; diminution
  2. maths a negative increment
  3. physics a measure of the damping of an oscillator, expressed by the ratio of the amplitude of a cycle to its amplitude after one period
  4. (of spectra) a sequence of related spectrum lines decaying in intensity, e.g. Balmer decay

Word Origin for decrement

C17: from Latin dēcrēmentum, from dēcrescere to decrease
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Word Origin and History for decremental

decrement

n.

1620s, from Latin decrementum "diminution," from stem of decrescere (see decrease).

Online Etymology Dictionary, © 2010 Douglas Harper