Rishon means first, former, or chief. It appears about 185 times. It describes chronological primacy, positional priority, and the 'former things' versus the 'new things' God does.
God is 'the First and the Last' (Isaiah 44:6) — absolute priority and ultimacy. The 'former things' prophesied have come to pass, and God declares 'new things' (Isaiah 42:9). The first covenant gives way to the new. Christ is the 'firstborn over all creation' (Colossians 1:15).