* A misspelling: Perhaps you meant "omni", which is a prefix meaning "all" or "everything".
* A slang term: It's possible "omnish" is a slang term used in a specific community or context. Without more context, it's impossible to say for sure.
* A made-up word: You might have encountered this word in a fictional work or a specific online community where it has a unique meaning.
To understand the meaning of "omnish", please provide more context. For example, where did you encounter this word? What was the surrounding text or situation?