Learn how to say Diagnostical correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word diagnose:
identify the nature of (an illness or other problem) by examination of the symptoms:
two doctors failed to diagnose a punctured lung
identify the nature of the medical condition of:
she was finally diagnosed as having epilepsy
20,000 men are diagnosed with skin cancer every year
mid 19th century: back-formation from diagnosis