keystone

Despite the pile-up of particulars, Metcalfe knows he must find the lost poem, that it is the keystone without which the story crumbles into insignificance.

The orangutan is a keystone species and plays a vital role in maintaining the health of the ecosystem.

Sunflower sea stars are considered a keystone species, meaning they are critical in regulating the stability and diversity of their ecosystems.

"This is a keystone appointment for us and an integral part of our five-year strategy as we look to achieve sustainable success for our senior men's side," said Tierney.

"You targeted the police as a keystone of government power," he added.