Claim: a word ending in -y is most likely not a noun but an adjective.
Don't have my tagged corpus handy to check. Anyone have the stats on Parts-Of-Speech of words ending in y and assuming they don't end in -ly?
The first script found 29476 words ending in -y, of which 13677 were -ly. Therefore we are left with 15799 words ending in -y but not -ly. Among these words, only 2643 were adjectives.
Therefore our key result is 2643/15799 = 0.16729. Approximately 1 out of 6.
This did not incorporate word frequencies, and I suspected they would boost the ranking somewhat, as many of the -y nonadjectives were quite rare (for example otolaryngology, noun). Thus I edited the program to tally instances of each word from a COCA-derived frequency list.
This leads to a frequency of 1632165/18057879 = 0.090385. Roughly 9% of words ending in -y but not -ly were adjectives. Surprisingly, this result was even smaller. I guess in the scheme of things "traditionally-suffixed" adjectives aren't really that common.
From the data I also found the converse question (does being an adjective generally imply a -y ending?). There were 28426173 total instances of adjectives and 2134139 adjectives ending in -y, including -ly. The result here was quite similar: 0.075077. Only about 3 out of every 40 adjectives have the "traditional" suffix.
Frequency results (percent) using WRI curated data.
The columns add up more than 100% because the same word can be accounted for in several rows.
Just as a reference, I used the following scripts (only one shown, Mathematica code):