There is some debate as to whether this word really exists. Wikipedia has removed it from a list of psychological terms still-to-be-defined, as the person looking for it couldn't find it in any reputable dictionaries. However, I (ChrisHowlett) came across the word in the concise OxfordEnglishDictionary? - not, admittedly, as an entry in its own right, but in a feature box on words ending in -phobia. The definition given there was actually "Fear of peanut butter sticking to the roof of one's mouth".
I thought Arachno- was to do with spiders. Or is that Arachna-? -- Garbled
It is. It seems to do double duty in many languages. Incidentally, other sources spell this word "Arachni-". --CH