What does CUK stand for?

Cause Unknown - Medicine (EDAA)

Chirurgische Klinik und Poliklinik (SAUS)

Combika - Sao Paulo, Brazil - Airport symbol (AD)

Custom Craft Pontoons, Lake Havasu, AZ - Manufacturer code for watercraft hull identification number (USCG)

Polo Aviation Ltd. - British - FAA designator (FAAC)

San Blas Kuna - Language code (ETLW)