News report by (almost entirely) nonsense host! (8)
I believe the answer is:
bulletin
'news report' is the definition.
(bulletin is a kind of news report)
'almost entirely nonsense host' is the wordplay.
'almost entirely' means to remove the last letter.
'nonsense' becomes 'bull' (I've seen this before).
'host' becomes 'letin' (to let someone into something is to host them).
'bull' with its last letter taken away is 'bul'.
'bul'+'letin'='BULLETIN'
'by' acts as a link.
(Other definitions for bulletin that I've seen before include "Official news item" , "Short official statement of news" , "Broadcast summary of news" , "Brief report issued to the public" , "News report" .)