Voluntary, intentional, deliberate, willful, willing can mean constituting or proceeding from an exercise of free will.
Voluntary , the most widely applicable of these terms, often implies not only freedom from constraint but freedom from the control of an influence that might suggest, prompt, or incite action; it does not necessarily imply that these influences have not been operative, but it usually suggests that the decision is the result of one’s free choice.
Often the term carries another, sometimes a different, implication, such as that of spontaneity or, especially when the opposition is to involuntary , that of subjection to or regulation by the will or that of prior consideration and clear choice <voluntary manslaughter> or that of absence of any legal obligation or compulsion (as to do or make) or of any valuable consideration in return for doing or making.
Intentional applies chiefly to acts or processes entered into in order to achieve a desired end or purpose or to the end or purpose so willed or effected; the use of the word eliminates all suggestion of the possibility of accident or inadvertence.
Deliberate (see also DELIBERATE 2 SLOW ) adds the implication of full knowledge or full consciousness of the nature of one’s intended act and a decision to go ahead in spite of such knowledge or consciousness.
Willful (see also UNRULY ) adds to deliberate the implications of a refusal to be taught, counseled, or commanded, and of an obstinate determination to follow one’s own will or choice in full consciousness of the influences or arguments opposed to the attitude adopted or the action or deed contemplated.
Willing carries, in contrast, an implication of characteristics (as agreeableness, openness of mind, or absence of reluctance) that makes one ready or eager, without suggestion or without coercion, to accede to the wishes or instructions of others or to do something or effect some end pleasing to them.