Appropriacy or appropriateness?

This morning, I was putting together the slides for a webinar about teaching academic vocabulary I'm doing on Thursday and in talking about the choices learners make when deciding which is the best word to use, I had a category that included ideas such as register and connotation, i.e. the most appropriate word for the context. I wanted a general heading for this section, but then came to a stop over whether to use appropriateness or appropriacy. My first instinct was that appropriateness felt a bit awkward and cumbersome to say, whereas appropriacy felt neater, more concise. As a "language professional" though I'm always wary about making silly linguistic gaffes, so I thought I'd better check. 

I checked the Oxford Advanced Learner's Dictionary first and, slightly to my relief, found it includes both - so I wasn't going completely mad. Oddly though, appropriacy has its own entry (with two senses; 1 "the extent to which something is suitable acceptable", 2 "the extent to which a word or phrase sounds correct and natural in relation to the situation it is used in"), whereas appropriateness is just a run-on at the end of appropriate. Unsure as to whether there was some difference of meaning or usage that I was missing, I went to the OED online and I was rather taken aback to find that appropriacy doesn't feature at all there! Now, my interest piqued, I went on to check Collins online and this time it was there, but interestingly, only in the sense of the right word for the context. I was tempted at this point to head off and consult a corpus, but with more pressing things to be done, I resisted the urge!

In such circumstances, I usually have confidence in my own intuition, provided I know I'm not completely wrong. Somehow this time though, I wavered and went for the "safer" option. Thus I now have a slide headed appropriateness, which I just know I'm going to stumble over pronouncing ...

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