What is the definition of the word Islam, and how was our master Abraham a Muslim before the coming of our master Muhammad, peace be upon him?

Ibn Kathir defined Islam as the only religion acceptable to Allah, which involves following the messengers in what they were sent with, the last of whom was Muhammad (peace and blessings of Allah be upon him). So, whoever meets Allah after his mission with a religion other than his law, it will not be accepted. All prophets shared one religion, which is Islam, as the Prophet (peace and blessings of Allah be upon him) said: "The prophets are paternal brothers; their mothers are different, but their religion is one." And Ibrahim (Abraham) (peace be upon him) was a Hanif (monotheist) and a Muslim.