flame, blaze
焔 centers on a visible, burning fire: a flame or blaze. The two meanings are nearly synonymous, both describing the bright, hot, gaseous part of a fire.
焔 is a variant form of 炎, with 火 (fire) on the left and a right side that likely developed from a phonetic or decorative element. The exact historical development of the right component is uncertain.
The left side is 火 (fire), and the right side looks like a container or enclosure. Imagine a fire burning inside a brazier or lamp, producing a steady flame.
For エン, picture the flame as the end of a candle wick: end -> エン, and the fire burns brightly at the tip.
dadaiko drum (decorated with flames)