Gaunt old American put onto man in saloon (10)
I believe the answer is:
'gaunt' is the definition.
'old american put onto man in saloon' is the wordplay.
I cannot really see how this works, but
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is located in the answer.
'american' could be 'us' (abbreviation for United States) and 'us' is found in the answer.
'man' could be 'dav' and 'dav' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for cadaverous that I've seen before include "Gaunt" , "not looking healthy" , "Unhealthy-looking" , "Corpse-like" , "Resembling a corpse" .)