"Lord, master" is nb in Egyptian, and Nile is usually written as itrw (literally "river"). Although Egyptian sometimes used an indirect genitival construction with a preposition (nb n itrw), it's easier to simply use the direct genitival construction nb itrw, "lord (of the) river." I've posted the hieroglyphs here. The far left sign (a basket) is the nb hieroglyph, the reed leaf is the uniliteral sign i, the semicircle (a bread loaf) is the uniliteral sign t, the mouth is the uniliteral sign r, the quail chick is the uniliteral sign w, and the last hieroglyph is a water determinative.