The same is true for writing. Every human language has been shaped by and changes to meet the needs of its speakers. Our language profoundly conditions our thought processes and shapes how we perceive and experience the world around us. The meanings we give to words are purely arbitrary, arrived at by social convention. There is no relation between signs and what they signify.
All linguistic signs are arbitrary.
Meanings of words are relational. No word is ever defined in isolation from other words. We use words to define other words. We are always working within the system of language itself. Cannot step outside of it.