Correct Spellings: DevaNagari, DevNagari
Devnagari and Devanagari both are the transliterated spellings of देवनागरी. Some people argue that 'Devnagari' is incorrect spelling. It is not.
The brain storming I did, resulted in the following finding!
'व' (v) is not a pure consonant but a semi-vowel! Its pronunciation is in between vowel 'उ' (u) and vowel 'अ' (a). So adding a vowel 'अ' (represented by 'a') is not desperately required after 'v'.
Moreover how a spelling (Devnagari, i.e.) which is used by lot of people can be called incorrect.
But most netizens prefers the spelling - 'Devanagari'.
If you ask me which spelling should be preferred, whether 'Devnagari' or 'Devanagari'; my answer will be 'DevaNagari'. I write 'DevaNagari' instead of 'Devanagari' to emphasize that 'Nagari' is the important part of the word!
We may/should use 'Nagari' instead of 'DevaNagari' when we refer it many times as short form.
Incorrect Spellings of देवनागरी
Devnagri, Deonagari and Deonagri are incorrect spellings. Dewanagari is also incorrect!
Alternate transliterated spellings of देवनागरी
'Devanagaree' is not incorrect! Infact it is the correct spelling as per the generally accepted rules of transliteration from Nagari to Latin. And if you follow our rules for transliteration, you will write 'devanaagaree'.