dissent; disagreement; refusal
Formal noun/adjectival noun expressing strong objection, disapproval, or refusal. Often used in official or serious contexts.
I expressed my dissent to his proposal.
If you disagree, please say so clearly.
Compound of 不 (negative prefix) and 承知 (consent, knowledge). The exact historical derivation is uncertain, but the word has been used in formal Japanese to express non-consent.