Writing Feedback / Extended definition essay; Enigma, intro and outline [3]

Currently, my intro goes like this:

Everyone knows how it is, to encounter a situation that leaves one wondering how it happened.
According to Merriam-Webster, enigma is described as someone or something that
is difficult to understand or to explain. The term enigma is commonly used when
discussing about the world's mysteries, such as the occurrence of an abnormally cold
winter despite the global warming, unsolved disappearance of people or
the formation of crop circles; However, it was also used as the name of
a spook hardware due to it's complexity that people invested so much to solve.
Enigma may be defined as a puzzle or a dark riddle; although, little was it known,
that it also referred to a device that made a difference between victory and defeat to the Germans during WWII.

My problem is that, I lack resources that explains enigma as the "mystery, riddle". But i have lots of sources that refers to the Enigma machine(Ciphering coding machine).

How should I go with this essay?
Is my intro strong enough? If not, please help.
My outline is this :
I still have no main ideas, please help me on how i should go with this essay.

1.0 Introduction
1.1 Background information
1.1.1 Dictionary
1.1.2 Uses
1.2 Thesis Statement
2.0 Body
2.1 Main Idea #1
2.1.1 Sub idea
2.1.2 Sub idea
2.2 Main Idea #2
2.2.1 Sub idea
2.2.2 Sub idea
3.0 Conclusion