Star in danger beneath collapsed seat (8)
I believe the answer is:
asterisk
'star' is the definition.
('asterisk' can be a synonym of 'star')
'danger beneath collapsed seat' is the wordplay.
'danger' becomes 'risk' ('risk' can be a synonym of 'danger').
'beneath' says to put letters next to each other (in a down clue).
'collapsed' indicates anagramming the letters.
'seat' is an anagram of 'aste'.
'risk' put after 'aste' is 'ASTERISK'.
'in' acts as a link.
(Other definitions for asterisk that I've seen before include "Character drawing attention to footnote" , "Textual reference symbol" , "star-shaped figure" , "Printed star" , "Star on a page" .)