clar ‧ i ‧ on call /ˈklæriən ˌkɔːl $ -ˌkɒːl/ BrE AmE noun [countable] formal
[ Date: 1800-1900 ; Origin: clarion type of trumpet (used for battle signals) 1300-1400 Medieval Latin clario , from Latin clarus ; ⇨ ↑ clear 1 ]
a strong and direct request for people to do something:
This election is a clarion call for our country to face the challenges ahead.