Is "shopaholic" a real word?

Question:I need to make sure it is because I want to use it in a college essay, but according Microsoft word, it is not. Does that mean that it is slang? Is it okay for me to use it in an essay for admissions? If it is, can you include a reliable source so that I can have a piece of mind? Thanks!

Answers:
According to http://www.m-w.com/dictionary/shopaholic... it is a noun and is not listed as slang.

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