Word Dhamma is one of ancient word in India. Dhamma is pali or prakrut form of Sanskrit word Dharma. Word is even today used as nature or laws or as duty in India. For example, Raj Dharma is duties of king or government. Agni dharma is to burn meaning fire burns.
There are laws or rules pertaining to everything in universe but in the context of teaching of Buddha, only those related to mind, body and interaction between mind and body are called Dhammas.
Other laws or rules (e.g. water boils at 100 c ) do not help in pursuit of final goal of Nibbana so not considered as dhamma in teaching of Buddha.
Other meaning if word Dhamma -- Phenomenon, contents of mind. whatever mind acquires is also called Dhamma.
Whole teaching of Buddha is about understanding all dhammas ( by direct experience and not just intellectually) and living within framework of dhamma so teachings of Budhha is Dhamma..
May I be free from enmity, disease and grief . As I am, so also may my parents, preceptors, teachers, intimate and indifferent and inimical beings be free from enmity, disease and grief. May they be released from suffering .