Short answers, pulled from the story.
Henry More coined it in 1660. No equivalent term existed in the Greco-Roman period. More's usage was not rigorous by later standards; he condemned Islam as having hypocritical monotheism and excluded pantheists from the category.
Monotheism holds that only one God exists or is dominant. Henotheism allows worshipping one god while accepting that others may validly worship different gods. Monolatry recognises many gods but worships only one consistently.
Most scholars classify him as a monolatrist rather than a monotheist. He refused to worship any god but Aten and banned idols, but he did not actively deny the existence of other gods. After his death, Egypt reverted to traditional religion and he was remembered as a heretic.
Up to the 8th century BCE, Israelite worship included El, Baal, Asherah, and Astarte. Some scholars date the push toward monotheism to the late 8th century BCE, partly as a response to Neo-Assyrian aggression. The concept of Yahweh as sole God of the entire world first emerged among priests and scribes during the Babylonian exile after the fall of Judah.
Both traditions object to the Trinitarian doctrine that God is three persons. Judaism uses the term shituf for worship that is neither purely monotheistic nor outright polytheistic. Islam considers attributing divinity to a created being the only unpardonable sin named in the Quran.
Waaq is the singular sky deity of many Cushitic peoples in the Horn of Africa, with roots traced to at least the 5th millennium BCE. The Oromo still practice Waaqeffanna, and the annual Irreechaa festival dedicated to Waaq draws tens of thousands of people in Addis Ababa.