* It's a misspelling: Could you be thinking of a similar-sounding word? Providing more context (where you encountered the word) would help.
* It's a dialectal word: Greek has many dialects, and a word might exist in one but not be widely known.
* It's a proper noun: It could be a name or place name.
* It's from another language: It might be a word borrowed from another language and used informally in a Greek-speaking context.
Without more information, it's impossible to say what "manari" means.