in the matter of (used typically as the first word in the heading of an official document or to introduce a reference in a formal letter)

re: invoice 87

the chemical element rhenium

each of the lines in which light (and heat) may seem to stream from the sun or any luminous body, or pass through a small opening

a ray of sunlight came through the window

a straight line extending indefinitely in one direction from a point

the ray that runs from the centre of the circle to the point of tangency

a thing that is arranged radially

a broad flat marine or freshwater fish with a cartilaginous skeleton, winglike pectoral fins, and a long slender tail. Many rays have venomous spines or electric organs

(in tonic sol-fa) the second note of a major scale

the chemical element of atomic number 75, a rare silvery-white metal which occurs in trace amounts in ores of molybdenum and other metals

religious education (as a school subject)

(in the UK) Royal Engineers