rectilinear regression vs linear function

rectilinear regression and linear function both are nouns.

Word	Noun	Adjective	Verb	Adverb
rectilinear regression	Yes	No	No	No
linear function	Yes	No	No	No

rectilinear regression (noun)	linear function (noun)
the relation between variables when the regression equation is linear: e.g., y = ax + b	a mathematical function whose graph (in Cartesian coordinates with uniform scales) is a line in the plane.