|"A noble spirit embiggens the smallest man."|
Verb transitive & intransitive. Obsolete exluding dialectical. Mid-17th century.
[from BIG + -EN.]
Make or become big; increase.
It's funny when you hear a word, snort with derision because it doesn't sound like a real word, and then find out that it is a real word and you are, in fact, a bit of a numpty. It goes the other way too: I was at a party once and I asked a girl from the Caribbean if she had acclimatised to the English weather. "Have I what?" she snorted (it was definitely a snort). "Have I acclimatised? That's not a real word." Bizarrely, another girl standing within earshot interjected. "It is," she said with an exasperated roll of the eyes. "Yeah. Ed's weird like that." At that point I decided to go and find some other people to talk to, ones that didn't think the use of real worlds was weird (my apologies - it would seem I've been waiting many years to get this one of my chest).
So what's this all got to do with biggen? Well, like acclimatise (apparently), biggen just doesn't sound like a real word. Use it at your own risk, as it's bound to prompt derisory sneers and glances. It's similar to the quote from The Simpsons: "A noble spirit embiggens the smallest man." Jebediah Springfield apparently spoke these words and they were adopted as Springfield's town motto. Although a neologism written specifically for that episode (Lisa the Iconoclast), embiggen has since slipped into somewhat common (if jocular) usage, although it isn't yet recognised by the OED. Therefore, it might even be the case that, on your use of the word biggen, you might be corrected with: "Umm ... actually I believe you mean embiggen."
Interestingly, there is a phenomenon in which one tries to invent a neologism, or accidentally trips over a word and muddles it up (as in a spoonerism), but the end product does actually turn out to be a real word (often an archaic, obsolete or highly specialised word). This is termed 'a perfectly cromulent word', a phrase from the same episode of The Simpsons in which a character expresses doubt about embiggen, only for someone to assert that 'embiggen is a perfectly cromulent word'.
However, if you're just a semi-literate idiot that doesn't know basic English words, it does not qualify as a 'perfectly cromulent word' scenario. I mean c'mon! Acclimatise? Acclimatise? It's such a rudimentary (and cromulent) word! Bah!