Grassmann's law

Etymology
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Proper noun

 * 1)  A dissimilatory phonological process in Ancient Greek and Sanskrit, according to which an aspirated consonant loses its aspiration if it is followed by another aspirated consonant in the next syllable.
 * 2)  An empirical law about human colour perception, stating that chromatic sensation can be described in terms of an effective stimulus consisting of linear combinations of different light colours.