take (one) for dead
To mistakenly assume or believe that one is dead. The bandits took the woman for dead, but she survived and swore revenge against them all. I took the creature for dead, but it leaped up and bit me on the arm when I approached it.
taken for dead
appearing to be dead; assumed to be dead. I was so ill with the flu that I was almost taken for dead. The accident victims were so seriously injured that they were taken for dead at first.