fire

(かじ) A harmful blaze, like a forest- or house-fire.   $$$
 
(ほのお) A big but useful flame like a bonfire or auto da fe.
 
(かさい) A slightly more newspaper-ish word for a harmful blaze. Kids use 火事 but adults can use both 火事 or 火災.   NP
 
() Any kind of fire – even a small fire like a lit match.