Treaty
Antonyms for unison are - disharmony - discord
The opposite could be solution, agreement, amity, comity, accord, or peace.
Consonance means "sounding together," or agreement, harmony, accord. Compare dissonance and assonance.
acceding, accession, accommodation, accord, accordance, acknowledging, adjustment, affiliation, affinity, alliance, amity, approving, arbitration, arrangement, assenting, authorizing, bargaining, compatibility, compliance, complying, compromise, concert, concession, concord, concordance, concurring
accord, agreement, compromise, harmony, rapprochement, settlement http://thesaurus.reference.com/browse/reconciliation
Disharmony
The 'odd one out' of the four words in the question is... disharmony.
Words that are opposites (antonyms) of disharmony are agreement, peace, accord, and harmony.
Antonyms for unison are - disharmony - discord
Consensus, Agreement
A consanonce is to accord or have an agreement.
An accord is an agreement of opinion or action, or the spontaneous impulse to carry out an action, in terms of "doing something of one's own accord".
The agreement was signed in the city Kyoto (Japan).
Accord and agreement are synonyms. An international accord is an agreement in which the parties come from more than one country, often from many. NAFTA is one example of an international accord, It stands for North American Free Trade Agreement. This international accord is between the governments of Canada, Mexico and the US for the mutual benefit of all three nations. The Maastricht Treaty, signed in 1992, was the treaty that created the European Union and established the Euro as a transnational European currency.
understanding, goodwill, peace, friendship, concert, calmness, amity, agreement, unity, accord, harmony
Following President Trump's announcement of a US withdrawal from the 2015 Paris Agreement, Indian Prime Minister Modi told French President Macron that India would uphold its commitment to the agreement. India's environment minister, Harsh Vardhan, also said on Friday that his country remained committed to the accord regardless of the position of other nations. "As far as the Paris agreement is concerned … our government is committed irrespective of the stand of anyone, anywhere in the world," Vardhan told reporters in a reference to Trump's withdrawal from the Paris Accord.
approval, agreement, understanding, sanction, permission, allowance, accord