big kahuna
/ˌbɪɡ kəˈhuːnə/(also big kahoona)
noun
1In Hawaii: a prominent priest, sage, or healer. Compare kahuna. rare.
2 Surfing. (A name for) a particularly skilled or respected surfer.
3A person or thing of great importance or power.
Origin
Late 19th century; earliest use found in Leprosy in Hawaii. From big + kahuna.