A co-worker asked me a short while ago whether it was time to go home yet, and I remarked that going home time was approaching more quickly than usual because of the Fridayness of the day. My co-worker was a little dubious of this notion. "How do you measure Fridayness?" he asked. "I don't know," I confessed, but added, "how does one measure happiness?" We certainly have an intuitive feel for relative levels of happiness even if we don't have a metric for it. I don't see why Fridayness (or its opposite, Mondayness) should be any different in that regard.

As a footnote, I'm willing to entertain the notion that "Fridayness" should be spelled "Fridainess" on the grounds that the root word for "happiness" is "happy", but it sure looks weird.