I had to look up "abstruse". I understood it's meaning from context, but wasn't sure if it was a portmanteau of abstract and obtuse, or an actual word. I've honestly never heard it in my life, and wouldn't stop someone saying it in a sentence, but it did stop my reading.

That made me wonder, does the fact that you sometimes have to listen to the spoken word over-estimate the impact the same words will have when written?