'selenium-deficient' originates from the word 'selenium,' which is derived from the Greek word 'selene,' meaning 'moon,' combined with the Latin word 'deficient,' meaning 'lacking.'

'Selenium' was named in the early 19th century, and 'deficient' has been used in English since the late Middle Ages. The combination 'selenium-deficient' is a modern term used in medical and nutritional contexts.

Initially, 'deficient' meant 'lacking' in a general sense, but in combination with 'selenium,' it specifically refers to a lack of this particular mineral.