linear regression vs rectilinear regression

linear regression and rectilinear regression both are nouns.

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

As nouns, linear regression and rectilinear regression are synonyms defined as:

linear regression and rectilinear regression: the relation between variables when the regression equation is linear: e.g., y = ax + b

linear regression (noun)	rectilinear regression (noun)
the relation between variables when the regression equation is linear: e.g., y = ax + b	the relation between variables when the regression equation is linear: e.g., y = ax + b