If my memory serves me correctly, I first encountered the word embiggen a year or so ago. I thought it seemed odd, but in context, the meaning was quite obvious.
Since that time I've seen this word with progressively greater frequency. I tried to Google the word and I can find references to it in both Wiktionary and the Urban Dictionary-- both are not professional, formal dictionaries so that would lend me to believe that the word is certainly slang.
However, in almost every context that I have observed this word in use, it has been within a professional or semi-formal environment.
Is embiggen considered a formal or slang word?