Definition of palatal law
: a statement in historical linguistics: Indo-European guttural consonants become palatals in Indo-Iranian when followed by the palatal vowel i or by an a which is equivalent to Greek and Latin e but remain gutturals when followed by the guttural vowel u or by an a which is equivalent to Greek and Latin a or o, thus establishing the a, e, and o found in the European languages as original Indo-European
