Figure out the rule that groups the images into pairs and connect them with straight lines. The answer is a single word.
The connection is
that some of the images are "double" other images. For instance, in the top right we have comic character TINTIN; at the bottom, we have TIN.
The completed drawing, with all images identified:
the uncrossed letters read EXTINCT BIRD: given the theme of doubled words, this must refer to the DODO! So the answer to the puzzle is DODO (or perhaps DO).