involuntary

Fernald has no entry of its own for involuntary; he lists it under spontaneous.

Where he writes about it:

That is spontaneous which is freely done, with no external compulsion and, in human actions, without special premeditation or distinct determination of the will; that is voluntary which is freely done with distinct act of will; that is involuntary which is independent of the will, and perhaps in opposition to it; a willing act is not only in accordance with will, but with desire. — from spontaneous

Thus voluntary and involuntary, which are antonyms of each other, are both partial synonyms of spontaneous. — from spontaneous

We speak of spontaneous generation, spontaneous combustion, spontaneous sympathy, an involuntary start, an unbidden tear, voluntary agreement, willing submission. — from spontaneous

A babe's smile in answer to that of its mother is spontaneous; the smile of a pouting child wheedled into good humor is involuntary. — from spontaneous

In physiology the action of the heart and lungs is called involuntary; the growth of the hair and nails is spontaneous; the action of swallowing is voluntary up to a certain point, beyond which it becomes involuntary or automatic. — from spontaneous

In the fullest sense of that which is not only without the will but distinctly in opposition to it, or compulsory, involuntary becomes an antonym, not only of voluntary but of spontaneous; as, involuntary servitude. — from spontaneous

A spontaneous outburst of applause is of necessity an act of volition, but so completely dependent on sympathetic impulse that it would seem frigid to call it voluntary, while to call it involuntary would imply some previous purpose or inclination not to applaud. — from spontaneous