Meaning of the word nonplussed in English

What does nonplussed mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

nonplussed

US /ˌnɑːnˈplʌst/
UK /ˌnɒnˈplʌst/

Adjective

surprised, confused, and not certain how to react:

Example:
I was completely nonplussed by his reply.