ダン, ノン, あたた.か, あたた.かい, あたた.まる, あたた.める

warmth

JLPT1 G6 S13 F1371

Two once-separate characters combine # (soft) + fire or sun/day, respectively → warm up and soften (by fire or by sunlight; compare the right-hand element of ) → *warm/heat up*. The present form, which has assumed this meaning from the others mentioned, combines sun/day + .

[Full Kanji Etymology List]