edge
渕 centers on the edge or border of something, especially a body of water. The meaning extends naturally to any rim or brink.
渕 is a variant form of 淵. It combines 氵 (water) with a right side that likely represents a deep pool or abyss, from which the idea of an edge or border derives. The exact historical development of the right-side components is uncertain.
Water 氵 flows beside a structure that looks like a gate 关 with a knife 刂 cutting its edge. Picture a sharp waterline where the water meets the shore: that's the edge.
For エン, imagine standing at the water's edge and seeing the end of the land: end -> エン, right where the water begins.