Instigate, v. t. [imp. & p. p. Instigated; p. pr. & vb. n. Instigating.]
Etymology: [L. instigatus, p. p. of instigare to instigate; pref. in- in + a root akin to G. stechen to prick, E. stick. See Stick.]
To goad or urge forward; to set on; to provoke; to incite; -- used chiefly with reference to evil actions; as to instigate one to a crime. He hath only instigated his blackest agents to the very extent of their malignity. Bp. Warburton.
Syn. -- To stimulate; urge; spur; provoke; tempt; incite; impel; encourage; animate.
Shades of meaning
Fernald has no entry of its own for instigate; he lists it under abet, influence.
Where he writes about it:
Abet and instigate are now used almost without exception in a bad sense; one may incite either to good or evil. — from abet
Abet and instigate apply either to persons or actions, incite to persons only; one incites a person to an action. — from abet
A clergyman will advocate the claims of justice, aid the poor, encourage the despondent, support the weak, uphold the constituted authorities; but he will not incite to a quarrel, instigate a riot, or abet a crime. — from abet
The originator of a crime often instigates or incites others to abet him in it, or one may instigate or incite others to a crime in the commission of which he himself takes no active part. — from abet
Incite and instigate, to spur or goad one to action, differ in the fact that incite may be to good, while instigate is always to evil (compare abet). — from influence