Definitions:
the point or position at an equal distance from the sides, edges, or ends of something

the form or voice of a verb expressing reflexive or reciprocal action.

at an equal distance from the extremities of something; central

denoting a voice of verbs in some languages, such as greek, which expresses reciprocal or reflexive action.

(in cricket, tennis, etc.) strike (the ball) with the middle of the bat, racket, or club