Oh, there are lots! They're called unpaired words: either words that sound like they should have a related word and do not, or whose related word has fallen into dialectical obscurity. "Nonplussed" is an example of the former, coming from the Latin non plus, meaning "no more." Meanwhile, "feckless" is the latter, because while the works of Thomas Carlyle brought "feckless" into general usage, the opposing "feckful" remains limited to Scottish English.
I did similar, and then it clicked in my mind after typing it. We use ruthless, but not ruth (I'm getting a red line under it as it's lower-case). Nonplussed and plussed is the same - we use the antonym, but not the original word.
"Nonplussed" is actually a little different, in that there is no original "plussed." It was formed directly from the Latin non plus, meaning "no more."
Chambers is not a random dictionary - it's the de-facto standard British dictionary for crossword compilers (and was the official Scrabble dictionary until 2005) - because it covers less conventional/slangly terms that other dictionaries didn't until online versions superceded paper ones.
Despite being British, Chambers is fine with North American slang - and has the following entry for john (that would be better for this quiz):
john noun, N Amer colloq (usually the john) a lavatory.
That one's a bit weird because it's deuterocanonical.
I mean: you could still make a decent case for it being included here, sure, but if I had to guess, that's probably why it's not. This site being what it is, you'd almost certainly get a good number of Protestants (and others) complaining that that's not a book of the Bible - and Quizmaster probably just doesn't want to deal with that.
Which is worth a trip to the smoggy streets of Los Angeles, where private eye Nick Danger walks ruthlessly. https://www.youtube.com/watch?v=RwG5c9IsgbA
And doggedly too, as you'll find out if you give it a listen.
Despite being British, Chambers is fine with North American slang - and has the following entry for john (that would be better for this quiz):
john noun, N Amer colloq (usually the john) a lavatory.
ETYMOLOGY: 20c: from the name John.
https://chambers.co.uk/search/?query=john&title=21st
I mean: you could still make a decent case for it being included here, sure, but if I had to guess, that's probably why it's not. This site being what it is, you'd almost certainly get a good number of Protestants (and others) complaining that that's not a book of the Bible - and Quizmaster probably just doesn't want to deal with that.
And doggedly too, as you'll find out if you give it a listen.