upright

Upright, erect, vertical, perpendicular imply that something is in the posture of being straight upward, not leaning. That which is upright is in a position corresponding to that of a person standing up: a decaying tree no longer standing upright; an upright piano. Erect emphasizes the straightness of position or posture: proud and erect; A flagpole stands erect. Vertical suggests upward direction, especially along the shortest line from the earth to a level above it: the vertical edge of a door; ornamented by vertical lines. Perpendicular, a term frequently interchangeable with vertical, is used especially in mathematics: the perpendicular side of a right triangle; to erect a perpendicular line from the base of a figure.