Newly arrived it is put back inside and reserved (8)
I believe the answer is:
reticent
'reserved' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for reticent that I've seen before include "Quiet" , "Not revealing one's thoughts readily" , "Reserved, not revealing thoughts readily" , "Reserved, shy" , "Close-lipped" .)