An Etymological Dictionary of Astronomy and Astrophysics

General: To regulate by or adjust to a certain measure or proportion; tone down. Physics: To alter the value of some parameter characterizing a periodic oscillation. → modulation.

Etymology (EN): From L. modulatus pr.p. of modulari “to regulate, measure off properly,” from modulus “small measure,” diminutive of modus “measure, manner,” → mode.

Etymology (PE): Degarâhangidan, from degar “other, another,” denoting change,
variant digar
(Mid.Pers. dit, ditikar “the other, the second;” O.Pers. duvitiya- “second,” Av. daibitya-, bitya- “second;” Skt. dvitiya- “second,” PIE *duitiio- “second”)

• âhang “melody, pitch, tune, modulation” (ultimately from Proto-Iranian *āhang-, from prefix ā-
• *hang-, from PIE base *seng^wh- “to sing, make an incantation;” cf. O.H.G. singan; Ger. singen; Goth. siggwan; Swed. sjunga; O.E. singan “to chant, sing, tell in song;” maybe cognate with Gk. omphe “voice; oracle”) +
  -idan infinitive suffix.