Magic star in confinement put on a little weight (9)
I believe the answer is:
pentagram
'magic star' is the definition.
'pentagram' can be an answer for 'star' (pentagram is a kind of star). I'm unsure of the 'magic' bit.
'confinement put on a little weight' is the wordplay.
'confinement put' becomes 'pent' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' says to put letters next to each other.
'little weight' becomes 'gram'.
'pent'+'a'+'gram'='PENTAGRAM'
'in' is the link.
Can you help me to learn more?
(Other definitions for pentagram that I've seen before include "magical symbol" , "Five-pointed star" , "Mystical symbol" , "Star-shaped figure" , "Five pointed star" .)