Headstrong, a.
1. Not easily restrained; ungovernable; obstinate; stubborn. Not let headstrong boy my will control. Dryden.
2. Directed by ungovernable will, or proceeding from obstinacy. Dryden.
Syn. -- Violent; obstinate; ungovernable; unratable; stubborn; unruly; venturesome; heady.
Shades of meaning
Fernald has no entry of its own for headstrong; he lists it under obstinate.
Where he writes about it:
The headstrong person is not to be stopped in his own course of action, while the obstinate and stubborn is not to be driven to another's way. — from obstinate
The headstrong act; the obstinate and stubborn may simply refuse to stir. — from obstinate
The unyielding conduct which we approve we call decided, firm, inflexible, resolute; that which we condemn we are apt to term headstrong, obstinate, stubborn. — from obstinate