ad. In a spontaneous manner; naturally; voluntarily.
The Century Dictionary and Cyclopedia
In a spontaneous manner; with spontaneity.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
ad. in a spontaneous manner
ad. without advance preparation
Word Usage
"The bottom line for all of this is the multifaceted observation that atoms join spontaneously to form molecules, consistent with energy relationships."