'Surprise!', like host in broadcast (8)
I believe the answer is:
astonish
'surprise' is the definition.
(I've seen this before)
'like host in broadcast' is the wordplay.
'like' becomes 'as'.
'broadcast' is an anagram indicator.
'host'+'in'='hostin'
'hostin' with letters rearranged gives 'tonish'.
'as'+'tonish'='ASTONISH'
(Other definitions for astonish that I've seen before include "Confound" , "Startle" , "electrify" , "Greatly surprise, amaze" , "Provoke wonder" .)