(comparative more nonplussed, superlative most nonplussed)
In recent North American English nonplussed has acquired the alternative meaning of "unimpressed". In 1999, this was considered a neologism, ostensibly from "not plussed", although "plussed" by itself is not a recognized English word. The "unimpressed" meaning is not considered standard usage by at least one authoritative source.
- simple past tense and past participle of nonplus
From Latin non plus (“no more, no further”).