NON'PLUS, noun [Latin not, and plus, more, further.] Puzzle; insuperable difficulty; a state in which one is unable to proceed or decide. NON'PLUS, verb transitive To puzzle; to confound; to put to a stand; to stop by embarrassment. Your situation has nonplussed me.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI