From WordNet (r) 3.0 (2006):
linear
adj 1: designating or involving an equation whose terms are of
the first degree [syn: linear, additive] [ant:
nonlinear]
2: of or in or along or relating to a line; involving a single
dimension; "a linear measurement" [syn: linear, one-
dimensional] [ant: cubic, planar, three-dimensional,
two-dimensional]
3: of a circuit or device having an output that is proportional
to the input; "analogue device"; "linear amplifier" [syn:
analogue, analog, linear] [ant: digital]
4: (of a leaf shape) long and narrow [syn: linear, elongate]
5: measured lengthwise; "cost of lumber per running foot" [syn:
linear, running(a)]