a.

1. 自發的；非出於強制的
   He made a spontaneous offer of help.

   他自願提供幫助。

2. （動作等）無意識的，不由自主的
   Hearing the joke, we burst into spontaneous laughter.

   聽到笑話，我們不由自主地大笑起來。

3. 自然的
   spontaneous behavior

   自然的舉止

4. （植物）自生的，非人工栽培的
5. （文體等）自然而優美的

adj.

1. performed or occurring as a result of an unpremeditated inner impulse and without external stimulus.
   ▸(of a process or event) occurring without apparent external cause.
   ▸Biology  (of movement or activity) instinctive or involuntary.
2. open, natural, and uninhibited.
3. archaic (of a plant) growing naturally and without being tended or cultivated.