spontaneous
used in Murder On The Orient Express

only 1 use

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Definition

behaving in an instinctive, uninhibited manner

or:

happening naturally (without planning or external force)

But it will be a point in your favour if it comes from you spontaneously.
3.8 — Part 3 Chapter 8 — Further Surprising Revelations (13% in)

There are no more uses of "spontaneous" in Murder On The Orient Express.

Typical Usage (best examples)