(bound form) front; forward; ahead; facing direction. Use 前边 qián​bian or 前面 qián​miàn for the standalone noun.

to stick out or protrude; convex; describes a male connector. This is the opposite of 凹 āo.

(bound form) back; rear; behind; in the direction of one's back

(colloquial) to stick up or bend upwards at one end; to tilt or rise up