muslim have an early meal before they fast, and they eat the meal around 3 to 5 AM or before sunrise. do you know specific word of this "early meal"?
If you're asking, "What is a single word for a pre-dawn meal that would be understood by English-speakers who are not familiar with Muslim traditions?" then I'm afraid there isn't one since fasting during daylight hours is not a common observance for non-Muslims. The best you could do is use the phrase pre-dawn meal.
If you're asking, "What is the word used by English-speaking Muslims?" then the answer is, "it depends." Generally, it's something derived from "Sahūr", but the exact spelling varies a lot between different populations with different ethnic and language backgrounds.
Wikipedia lists several name variations, and there "Suhoor" is listed as a UK variant. Here in Toronto, there's a blog called "Halal Foodie" that has an annual Toronto Ramadan Restaurant Iftar and Suhoor Guide. So that's two data points in favor of Suhoor as the Anglicized version. But I don't have to look very hard to find Toronto-based English-language pages that use other variants like Sahur or Sehri (those seem to be used by communities with Arabic or Bengali/Urdu backgrounds, respectively).