Crossword Genius

It's an arm, not the head, that adapts slowly (7)

Ross

I believe the answer is:

article

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

This could be a double definition.

'it's' is the first definition.
(I've seen this before)

'an arm not the head that adapts slowly' is the second definition.
'article' can be an answer for 'an'. I am not certain of the rest of the definition.

Can you help me to learn more?

(Other definitions for article that I've seen before include "Feature - item" , "See 10" , "Newspaper item" , "What journalist writes" , "Object - piece of writing" .)

I've seen this clue in The Times.
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