Being very important, or key to something.
Having or containing the centre of something.
Being in the centre.
Exerting its action towards the peripheral organs.
centre
Of the highest rank or position; of the greatest importance; of the highest priority.
Positioned in front of (all) others in space, most forward.
Coming before (all) others in time.
Closest to the bow.
In front, prominently forward.
First in time.
Most importantly.