The word that matches the meaning of the word “gold” in the first life is nature's “first green”.
Explanation
Through a poem of only eight lines, Robert Frost's 'Nothing gold can stay' conveyed a significant message through metaphors.
Here the word 'gold' is used for 'first green' has nothing to do with the color comparisons instead he shows that nature's first green budding leaf during the spring season is equivalent to the value of sight of gold.
But with time this green fades away.