noun, noun which may take the genitive case particle 'no'
Refers to a geometric straight line or something linear; also used attributively with の to mean 'straight' or 'direct'.
Please draw a straight line using a ruler.
This road continues in a straight line to the station.
I drew a straight line in my notebook to make a graph.
I connected point A and point B on the map with a straight line.
This road goes straight ahead for a while.
直線 means a straight line, the opposite of 曲がり, which describes a bend or curve.
直線 means a straight line, the direct opposite of a カーブ, which is a curved or bending line.
linearity
linear; straight-line · straightforward; simple; direct