like an arrow

consecutive nonstop short smooth solid straightforward successive true

beeline direct even horizontal invariable level perpendicular plumb right running square upright vertical

collinear continuous erect in a line in a row in line inflexible lineal linear near precipitous rectilineal rectilinear sheer through unbent unbroken uncurled undeviating undistorted uninterrupted unrelieved unswerving

broken incontinuous intermittent

level uneven varying

curved twisted