Crossword Genius

In essence first character goes back to the previous season (6)

Ross

I believe the answer is:

mature

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'season' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for mature that I've seen before include "Fully grown and developed (6)" , "due to be paid" , "sensible" , "reach the end of term" , "Old film star" .)

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