Suppressed thorium decay before time was up (9)
I believe the answer is:
throttled
'suppressed' is the definition.
(I've seen this before)
'thorium decay before time was up' is the wordplay.
'thorium' becomes 'Th' (Th is the chemical symbol for thorium).
'decay' becomes 'rot' (rot can mean to decay).
'before' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'was up' becomes 'led' (I've seen this in another clue).
'th'+'rot'+'t'+'led'='THROTTLED'
(Other definitions for throttled that I've seen before include "Choked" , "Strangled manually" , "Suppressed" .)