1. Godan verb with 'ru' ending, Intransitive verb

   to smoke; to smoulder; to smolder; to sputter

   Usually written using kana alone

   くすぶっていた薪が突然燃え上がった。

2. to be sooty; to be smoke-stained

   Usually written using kana alone

3. to smoulder (e.g. a dispute); to smolder

   Usually written using kana alone

4. to seclude oneself

   Usually written using kana alone

5. to live in obscurity; to stay in the same level (of social position, circumstances, etc.)

   Usually written using kana alone

Also written 燻ぶる【くすぶる】kusuburu