South American writer on large body of water? Without a doubt (8)
I believe the answer is:
suspense
'doubt' is the definition.
(I know that suspense is a type of doubt)
'south american writer on large body of' is the wordplay.
'south' becomes 's' (abbreviation).
'american' becomes 'US' (abbreviation for United States).
'writer on large body of' becomes 'pense' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
's'+'us'+'pense'='SUSPENSE'
'water? without a' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for suspense that I've seen before include "Seen puss (anag.)" , "Excitement and uncertainty about an outcome" , "Nervous uncertainty; cessation" , "Doubt" , "State of anxiety while waiting" .)