Suppository is one of those words that I would assume 99.9% of the population knows because of it being common over the counter, and in sitcoms and media. I'm assuming they're including children under 12 in the data? That would explain the low percentages.
More people are functionally illiterate than you might expect if you're in a high IQ bubble like the tech industry. In 2017, 19% of American adults scored level 1 or below on the PIAAC literacy test: https://nces.ed.gov/fastfacts/display.asp?id=69
If the US has so many non-English speakers that it materially affects national literacy statistics, one might wonder how we ended up with an immigration policy that produces a permanent underclass of people who are locked out of meaningful jobs and are entirely outside the protection of the law, due to being in the country illegally.
I had no idea what a suppository is, but I do recognise pessary. But that's probably because suppository is completely different in Dutch, which is not the case for pessary.
That checks out. I'd say at least 80% of my encounters with the word have been jokes in media, or jokes between people (probably inspired by or ripped off from media). Most young kids wouldn't know it, though.
If it's the same as the Dutch word "pessarium", I think it's a form of birth control. Got mentioned in sex-ed in school, though obviously not something I (as a man) ever had to use. I guess it makes sense for women to be more familiar with a device that only women ever use.
