Meaning of Grassman's law

Grass'man's law'

Pronunciation: [key]
— Ling. Ling.
  1. an observation, made by H. G. Grassman, that when aspirated consonants occurred in successive syllables in Sanskrit and classical Greek, one, usually the first, was unaspirated, becoming a voiced stop in Sanskrit and a voiceless stop in Greek.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.