Who was it that gave Fāṭimah, the daughter of the the Messenger of God, peace and blessings be upon him, the title "al-Zahrāʾ", and what does it mean?

The title "al-Zahra'" is well-known among scholars, both ancient and modern. It was mentioned by Ibn Hajar in al-Isabah and by Ibn Hibban in several of his works. Its meaning is "whiteness." So, it is said: "a man is azhar" meaning he is white, intensely white with complete beauty, as if his light is radiating.