Is "ok" Okay?

I have a favorite kind of ballpoint pen at work: the Pilot G-2, blue. It's truly a beautiful pen. Being such an enviable pen, and being located at the front desk of my office, these pens often get stolen and are never seen again. This morning I found myself without my trusty blue G-2. So I got another one from the office supply shelf and am now constructing a tag, made from the sticky part of a neon pink Post-It note, to affix to the pen so as to be recognizable as not-one's-own to anyone who borrows it. As insurance, I decided to write a little note on the tag - something along the lines of "this is Sarah's - do not steal" or "stealing is a crime" or something like that. In search of a synonym for "steal," I went to thesaurus.reference.com and was shocked by what I found. The definition of "steal," as provided by Roget's New Millennium™ Thesaurus, reads "take without ok." I don't think I've ever seen the official definition of a word include the word "ok."
Though my credo is "language is dynamic," this was a truly unexpected find.