Does look Fabaceous. A big family, so it may not belong to any of the genera you listed. Maybe it will bloom comparatively small, and you will then be able to see what you have.

You might look up pea family genera to see if any have similar names to what the seed was supposed to be.

The seedling reminds me of a honey locust, but I'm not sure if the seed looks like what you have.

I did grow a gleditsia years ago in Melbourne and am pretty sure that gleditsia seeds are fuller, harder and more rounded than these, which are more flat--a little in shape and texture like pumpkin seeds. I forgot to mention that the seeds, although from a US seller, were shipped from India, so it is probably something that is commonly grown over there ... but that still leaves a wide field of choices.

I was looking at both of the threads, you mentioned they came from India. I just wanted to mention that the plant looks like Chamaecrista nictitans (Wild sensitive plant), which is in the Fabaceae family. It is an invasive grower over in India, I am not sure how big the seeds are though. Just another clue to help you in your search. :)

In that case, it's fortunate that it doesn't look to be a Chamaecrista nictitans, as the seed of that plant looks square shaped (see link below). Nice guess, though!

Here is a link that might be useful: {{gwi:143333}}