錬
レン, ね.る
tempering, refine, drill, train, polish
JLPT1 G7 S16 F2221
Originally 柬# (separate) + 金 metal → *refine* metal, separating out impure elements (compare 煉) → *temper*; *forge*; *train*. The present form replaces 柬 with 東.
[Full Kanji Etymology List]