The words we use to represent objects and actions in language have no necessary relationship to the meanings of the words. That is, the name of something is not related to its meaning. Other words or parts of words give just a hint of meaning. Different languages use different words for the same thing. The ancient Greeks argued about arbitrariness in language with Aristotle on the side of conventionalists, who posited that the speakers of a language decide on the meanings of words.
Convention is the dictionary of a language.
In English we add -ess to some words to form the feminine of that word. Give three examples from your native language.