The kanji 灰 primarily represents "ash" or "gray." It refers to the powdery residue left after something has been burned. It can also figuratively represent things that are dull or lackluster.

・On-yomi (音読み): かい (kai) ・Kun-yomi (訓読み): はい (hai)

⚫︎灰皿 Translation: ashtray ⚫︎灰色 Translation: gray color ⚫︎火山灰 Translation: volcanic ash

The kanji 灰 is a phono-semantic compound (形声文字, けいせいいもじ). The left side is the radical 火 (ひ, hi), meaning "fire," and the right side is the phonetic character 灰 (かい, kai), which is pronounced as "kai." The combination suggests something related to fire, in this case, the result of fire: ash. The original shape of the character depicted a person being burned by fire, and the residual ash.