The phrase "great arc" means a long or large curve or trajectory. It is often used to describe a sweeping or significant path or course. Full definition
The post-credits cameo of the big bad Thanos in The Avengers set into motion an even greater arc of ambition that catapulted two more phases, twelve more films, and dozens of new major players since. (everymoviehasalesson.com)
A woman's ankle can rotate through a much greater arc, one biologist has suggested, because our early female ancestors had to stretch from one branch to another while foraging in the trees and bushes, whereas heavier - bodied males tended to stick to flat land. (discovermagazine.com)
Hodgkin's images are intimate, thoughtful, and ultimately indescribable, yet they suggest great arcs of time and thought. (howard-hodgkin.com)