"When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean—neither more nor less."
After extensive research - I looked at maybe 3 online dictionaries - I concluded that dictionaries define science either as an organized body of knowledge or the process of assembling the same. I'm going to go with the process version, and since I'm doing the choosing here, and I'm calling economics a science. It's actually the senior member of the social sciences.
This is not a peculiar choice. The Nobel Memorial prizes are given in Economic Science, not Economic Art or Economic religion. The NSF has a division of economic sciences. Universities have departments of economic science.
The thing that make an activity a science, I think - I choose - is the systematic assembly and analysis of data. I would add two crucial ingredients for doing good science: honesty and a critical, especially self-critical, attitude. These latter two are not very natural to humans, but they are essential. Economists have been assembling such data for a few hundred years now, at least, and their is widespread acknowledgement of its usefulness. Moreover, they have formulated some principles that appear generally applicable. Of course there are also plenty of areas of controversy, as would be expected in any developing science.