"Cosmos” host Carl (5)
I believe the answer is:
sagan
'cosmos host carl' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sagan that I've seen before include "Author of Bonjour Tristesse, d. 2004" , "US scientist" , "French author" , "French authoress" , "Astronomer" .)