Hi,
that's an interesting question. Veeeery interesting. I've always wanted to ask about this...
I wonder how natives can read a word if they never heard it.
Can they (or we) read a book about medicine, pharmacy, etc. on their own? In theory, they need to go to college and hear a lecturer pronounce them. Or... how can they study Geography by themselves, if you can't even know how to pronounce the name of a town or city without hearing it at least once? (Example: Plymouth! Geez, when I heard that, I thought... Oh, yeah, that was easy to figure out! LOL)
So I'm thinking of those who study medicine, and have to learn thousands of weird terms, with weird pronounciations, and even weirder spelling (it's like writing in Latin). How can you remember that?
As for your question, Hitesh, if you can't find a word in the largest dictionaries (like Merriam-Webster)... there isn't much else that you can do, lol. But if it's a common word that you can't find (like a brand name), you can try searching with Google. Often you won't find anything though.