Group of stars holding cape's clingy fabric (5)
I believe the answer is:
lycra
'clingy fabric' is the definition.
(lycra is a tight-fitting material)
'group of stars holding cape's' is the wordplay.
'group of stars' becomes 'Lyra' (Lyra is a constellation).
'holding' means one lot of letters goes inside another.
'cape' becomes 'c' (abbreviation used on maps).
'lyra' enclosing 'c' is 'LYCRA'.
(Other definitions for lycra that I've seen before include "Synthetic fabric" , "Stretchy sports material" , "gear for cyclists" , "clinging fabric" , "Sports clothes fabric" .)