hem, margin, reason, cause, karma, fate
緣 centers on a connecting edge: a hem or margin that binds fabric, and by extension the ties of reason, cause, karma, or fate that link events together.
緣 combines 糸 (thread) with 彖, which likely contributes the sound and the idea of a decorative border or edge. The modern Japanese simplified form is 縁.
Thread 糸 runs along the edge of a garment, forming a hem. That hem is a boundary that connects the fabric, just as fate connects events.
For エン, picture the hem of a garment ending in a neat line: end -> エン, and that edge ties everything together like karma.