> By this reasoning Urdu is the most widely spoken language of India.
Exactly! Couldn't have worded it better.
अवश्य - Avashya
It is closer to "Certainly"
Yes, but I didn't say there was no word in formal Hindi that didn't mean the same thing as 'zaroor'. I said 'nishchit' isn't that word.
'Avashya' is again a word you wouldn't be able to use in colloquial speech without coming across as eccentric. It means the same thing as 'zaroor' but it's like saying "I am desirous of x" instead of "I want x".
My grandmother was illiterate, but I remember her using Avashya even when she did not speak Khari boli much
I've grown up in North India and have never word anyone speak the word "avashya" outside of a Hindi lesson. I can only assume your grandmother was using it as an exemplar for your benefit. Perhaps there are communities where it is spoken colloquially but by far the norm is "zaroor" or "jaroor" (same word but the sound has shifted in some places like Western UP from Z to J).
You can find examples of the use of "avashya" in the movies of Hrishikesh Mukherjee (like Golmaal and Chupke-Chupke) in which off-beat characters who made a special point of speaking the purest Hindi as part of their characters' eccentricity used "avashya" and other words like it, while the other characters who spoke normal Hindi didn't.
By this reasoning Urdu is the most widely spoken language of India.
'Nishchit' doesn't even by itself replace 'zaroor'. 'Nishchit' means certain or definite. To replace 'zaroor' (certainly or definitely) you would actually have to say 'nishchit roop se'.
Hindi-speaking people absolutely use 'zaroor' and 'bilkul' instead of 'nishchit roop se' when they're actually speaking Hindi, instead of self-consciously speaking Sanskritised Hindi in a formal register -- and this is always in the context of a specific political alignment.