Negotiate, v. i.
Etymology: [L. negotiatus, p.p. of negotiari, fr. negotium business; nec not + otium leisure. Cf. Neglect.]
1. To transact business; to carry on trade. [Obs.] Hammond.
2. To treat with another respecting purchase and sale or some business affair; to bargain or trade; as, to negotiate with a man for the purchase of goods or a farm.
3. To hold intercourse respecting a treaty, league, or convention; to treat with, respecting peace or commerce; to conduct communications or conferences. He that negotiates between God and man Is God's ambassador. Cowper.
4. To intrigue; to scheme. [Obs.] Bacon.
1 other Webster entry under this spelling
Negotiate, v. t. [imp. & p. p. Negotiated; p. pr. & vb. n. Negotiating.]
1. To carry on negotiations concerning; to procure or arrange for by negotiation; as, to negotiate peace, or an exchange. Constantinople had negotiated in the isles of the Archipelago ... the most indispensable supplies. Gibbon.
2. To transfer for a valuable consideration under rules of commercial law; to sell; to pass. The notes were not negotiated to them in the usual course of business or trade. Kent.
Shades of meaning
Fernald has no entry of its own for negotiate; he lists it under transact.
Where he writes about it:
To negotiate and to treat are likewise collective acts, but both these words lay stress upon deliberation with adjustment of mutual claims and interests; transact, while it may depend upon previous deliberation, states execution only. — from transact
Negotiate has more reference to execution than treat; nations may treat of peace without result, but when a treaty is negotiated, peace is secured; the citizens of the two nations are then free to transact business with one another. — from transact