Synonym: automatic, inherent, instinctive, natural. Antonym: compulsory. Similar words: simultaneously, respond, sponsor, response, respondent, a bone of contention, correspondent, spouse. Meaning: [spɑn'teɪnɪəs /spɒn-] 
adj. 1. happening or arising without apparent external cause 2. said or done without having been planned or written in advance.
adj. 1. happening or arising without apparent external cause 2. said or done without having been planned or written in advance. 
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1. The crowd gave a spontaneous cheer.
2. The eruption of a volcano is spontaneous.
3. Most of their music was spontaneous improvisation.
4. The audience burst into spontaneous applause.
5. His jokes seemed spontaneous, but were in fact carefully prepared beforehand.
6. Diana's house was crowded with happy people whose spontaneous outbursts of song were accompanied by lively music.
7. My spontaneous reaction was to run away.
8. I had another spontaneous miscarriage at around the 16th to 18th week.
9. When angered, Ellen was given to spontaneous outbursts, while her partner Terry would do a slow burn.
9. Sentencedict.com is a online sentence dictionary, on which you can find excellent sentences for a large number of words.
10. The group was greeted by spontaneous applause.
11. A spontaneous shiver of delight knifed through Mattie.
12. I'm trying to be more spontaneous.
13. Outspoken speeches were given which received spontaneous standing ovations.
14. Others manage better in a more spontaneous fashion.
15. They can also provide the spontaneous formation of gradients.
16. Her acting is completely spontaneous and uninhibited.
17. Statistics do not distinguish between induced and spontaneous abortions.
18. It may also inhibit spontaneous protest.
19. The spontaneous speech of such patients is often rambling.
20. Humans and other animals originally arose by spontaneous generation.
21. The congregation broke into spontaneous applause.
22. The invitation was completely spontaneous.
23. A few cases of spontaneous combustion.
24. Defence lawyers claimed that the shooting was a spontaneous reaction, ferocious[sentencedict.com], but not part of a plan.
25. With such spontaneous performances the players clearly enjoying themselves - the pieces are easy to enjoy.
26. The verb is spontaneous, fluid and not repeatable; the adjective is calculated, static and repeatable.
27. Also, full marks to the spontaneous half-time entertainment of gymnastics provided by the children in the audience.
28. In classical theory a spontaneous fall in the real wage rate is the initiating force tending to raise employment and output.
29. Our studies provided evidence of such relaxations during episodes of spontaneous gastro-oesophageal reflux in children.
30. The isotope U-235 is unstable, decaying by a process called spontaneous fission.
More similar words: simultaneously, respond, sponsor, response, respondent, a bone of contention, correspondent, spouse, espouse, be responsible for, corresponding to, courteous, on the spot, courageous, contain, intangible, container, fantabulous, confrontation, continuous, on the contrary, lane, panel, planet, mundane, keep on, airplane, hurricane, component, opponent.