Large Scale
noun, な adjective
Remember how 規模 is scale? Well, this is a big scale, which is on a large scale.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
細川は、原発再稼働に反対する大規模デモの実現に協力してくれたことについて、児島に礼を述べた。
Hosokawa thanked Kojima for helping him stage a large-scale rally against resuming nuclear power plant operations.