Meaning

adjective designating or involving an equation whose terms are of the first degree

adjective of or in or along or relating to a line; involving a single dimension

adjective of a circuit or device having an output that is proportional to the input

originBorrowed from Latin līneāris, from līnea (“line”) + -āris (adjectival suffix), equivalent to line + -ar. Doublet of lineal.

Etymology from Wiktionary, CC BY-SA 3.0