VOLUNTEE'R, a. Entering into service of free will; as volunteer companies.
VOLUNTEE'R, v.t. To offer or bestow voluntarily, or without solicitation or compulsion; as, to volunteer one's services.
VOLUNTEE'R, v.i. To enter into any service of one's free will, without solicitation or compulsion. He volunteered in that undertaking.
[These verbs are in respectable use.]