victim vs sitting duck

victim and sitting duck both are nouns.

Word	Noun	Adjective	Verb	Adverb
victim	Yes	No	No	No
sitting duck	Yes	No	No	No

As nouns, sitting duck is a hyponym of victim; that is, sitting duck is a word with a more specific, narrower meaning than victim:

Other hyponyms of victim include butt, goat, laughingstock, stooge, chump, fall guy, fool, gull, mark, mug, patsy, soft touch, sucker, lamb, easy mark.

victim (noun)	sitting duck (noun)
an unfortunate person who suffers from some adverse circumstance	a defenseless victim
a person who is tricked or swindled