One's left us for dead? (9)
I believe the answer is:
euphemism
'dead?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'one's left us' is the wordplay.
I cannot quite understand how this works, but
'one's' could be 'is' (roman numeral) and 'is' is present in the answer.
This may be the basis of clue (or it may be nonsense).
'for' acts as a link.
Can you help me to learn more?
(Other definitions for euphemism that I've seen before include "Mild term substituted for one less acceptable" , "sugar?" , "Indirect expression used in place of an offensive one" , "polite term" , "Inoffensive term used in place of one considered offensive" .)