Verb (5-dan, る, intransitive)
Usually written in kana
1.  to smoke;  to smoulder;  to smolder;  to sputter
2.  to be sooty;  to be smoke-stained
when read as "くすぶる, ふすぶる"
3.  to smoulder (e.g. a dispute);  to smolder
when read as "くすぶる"
4.  to seclude oneself
when read as "くすぶる, ふすぶる"
5.  to live in obscurity;  to stay in the same level (of social position, circumstances, etc.)
when read as "くすぶる"