暖める
あたためる · atatameru · JLPT N3 · verb-ichidan
to heat
🔥🍲 atatameru sounds like a tatami room you heat up: warm (it) up
暖 means warm, and the verb ending める makes it something you do to an object: you warm it up. Compare 暖かい (atatakai), meaning warm. Both share the atata- sound, so atata- marks the warm words.
暖 — sun radical 日 + 爰 (yuán, phonetic)
暖 is a semantic-phonetic compound. The 日 'sun' radical carries the meaning of warmth, while 爰 supplies the sound (historically close to 'nuǎn'). It originally described the warmth of sunlight and broadened to mean 'warm' in general — both physical heat and figurative warmth like kindness.