Most importantly.
In front, prominently forward.
First in time.
Positioned in front of (all) others in space, most forward.
Coming before (all) others in time.
Closest to the bow.
Of the highest rank or position; of the greatest importance; of the highest priority.
To a considerable degree, to a great extent.
With a great weight.
So as to be thick or heavy.
In a laboured manner.
In a manner designed for heavy duty.
In a heavy manner.