large fire; big fire; conflagration
Refers to a fire that is large in scale, often used in news or dramatic contexts. More emphatic than 火事 alone.
There was a large fire in the center of town last night.
Many houses burned down in the big fire.
Compound of 大 (おお, 'big') + 火事 (かじ, 'fire'). The reading おおかじ follows the kun'yomi of 大 and the on'yomi of 火事.