main ridge of a roof; top ridge
Refers to the highest horizontal ridge where two roof slopes meet, especially in traditional Japanese architecture.
大棟には鬼瓦が載っている。
An ogre tile sits on the main ridge of the roof.
Compound of 大 (おお, 'large, main') and 棟 (むね, 'ridge'). The reading おおむね is a straightforward kun'yomi combination.