Some fancy nickname for Cassandra (5)
I believe the answer is:
cynic
'cassandra' is the definition.
(thesaurus)
'some fancy nickname for' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'CYNIC' can be found hidden inside 'fancy nickname for'.
(Other definitions for cynic that I've seen before include "One who knows the cost of everything and the value of nothing" , "One who believes people's motives are always selfish" , "Sort of Greek philosopher" , "One believing all are motivated by self-interest" , "One who takes a pessimistic view of human goodness or sincerity" .)