Sensational start to lecture union leader delivered (5)
I believe the answer is:
lurid
'sensational' is the definition.
(similar in meaning)
'start to lecture union leader delivered' is the wordplay.
'start to' suggests taking the first letters.
'leader' indicates taking the first letters.
'delivered' becomes 'rid' (I've seen this in other clues).
The initial letter of 'lecture' is 'l'.
The first letter of 'union' is 'u'.
'l'+'u'+'rid'='LURID'
(Other definitions for lurid that I've seen before include "Melodramatic" , "Sensational or dazzling" , "Melodramatically sensational" , "Horrifying - sensational" , "Sensational; colourful" .)