One acted in terrible show (8)
I believe the answer is:
indicate
'show' is the definition.
('indicate' can be a synonym of 'show')
'one acted in terrible' is the wordplay.
'one' becomes 'i' (Roman numeral).
'terrible' indicates anagramming the letters.
'acted'+'in'='actedin'
'actedin' is an anagram of 'ndicate'.
'i'+'ndicate'='INDICATE'
(Other definitions for indicate that I've seen before include "Point out, suggest" , "Point out, make known" , "(Give a) signal" , "Point out or give some notion of" , "Make a signal" .)