Ask HN: What API do you wish existed?

[reggiepret]

You pass me four colors and I return a length? You pass me four songs and I return most frequently used words? You pass me three names and I return the meanings of them? You pass me three wedding registry items and I return links to all online shops that you can purchase them from?

I find that I need better metadata on some of my data points and would love some external API's that would provide me with the information.

Any suggestions?