Fully matured beef, we hear? (5)

I believe the answer is:

grown

I'm a little stuck... Click here to teach me more about this clue!

'fully matured' is the definition.
'grown' can be an answer for 'matured' (I've seen this before). I'm unsure of the 'fully' bit.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for grown that I've seen before include "Cultivated" , "Matured" , "Raised; having got bigger" , "Big" , "Fully developed" .)

I've seen this clue in The Guardian.

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