Here are some synonyms for spontaneous:
* Unplanned
* Impulsive
* Unexpected
* Unprompted
* Natural
* Instinctive
* Automatic
Here are some examples of how "spontaneous" is used:
* "We had a spontaneous picnic in the park."
* "She burst into spontaneous laughter."
* "The plant's growth was completely spontaneous."
* "The audience erupted in spontaneous applause."
It's important to note that "spontaneous" can have slightly different meanings depending on the context. For example, in chemistry, "spontaneous" refers to a reaction that occurs without the need for external energy.