Formal:
* गंभीर (gambhir): This is the most common and formal translation of "serious". It can be used in almost any situation.
* गंभीरता (gambhiratā): This is the noun form of "serious" and means "seriousness".
* गंभीर रूप से (gambhir rūp se): This means "seriously" in a formal way.
Informal:
* गंभीर (gambhir): This can also be used informally, but it might sound a bit too formal in casual conversations.
* गंभीर वाला (gambhir wālā): This means "serious one" and is a more informal way to say "serious".
* सीरियस (sīriyas): This is the Hindi transliteration of the English word "serious" and is often used in informal contexts.
Other options:
* गंभीरता से (gambhiratā se): This means "with seriousness" or "seriously".
* महत्वपूर्ण (mahatvapūrṇa): This means "important" and can be used in some contexts where "serious" is appropriate.
* जिम्मेदार (jimmedār): This means "responsible" and can be used when referring to someone who takes things seriously.
The best way to choose the right translation is to consider the context and the level of formality. For example, if you are talking about a serious illness, you would use a more formal translation like "गंभीर (gambhir)". If you are talking about someone who is being serious about their work, you might use a more informal translation like "गंभीर वाला (gambhir wālā)".