the straight and narrow

:  free from curves, bends, angles, or irregularities

:  generated by a point moving continuously in the same direction and expressed by a linear equation

:  lying along or holding to a direct or proper course or method

:  in a straight manner

:  straighten

:  something that is straight: such as

:  a straight line or arrangement

:  straightaway

:  of slender width

:  of less than standard or usual width

:  woven in widths usually less than 18 inches (46 centimeters)

:  to decrease the breadth or extent of :  contract

:  to decrease the scope or sphere of :  limit

:  to lessen in width or extent :  contract

:  a narrow part or passage