The word "mystique" originates from French, where it means "mystical" or "mysterious," and ultimately derives from the Latin "mysticus," which itself comes from the Greek "mystikos."   This Greek root is connected to the word "myein," meaning "to close" (as in the lips or eyes), and "mystes," meaning "one who has been initiated". The concept of mystique implies an aura of mystery, fascination, and perhaps even a hidden or esoteric quality surrounding a person, object, or idea. 

The earliest known use of the noun mystique is in the 1890s. OED's earliest evidence for mystique is from 1891, in a letter by Ernest Dowson, poet. 

Examples of "mystique" used in a sentence: 
"As a child, there was some mystique associated with a power outage." 
"These products are surrounded by considerable mystique and are often outrageously expensive." 
"No one has been able to copy the legendary singer's mystique." 
"There's a certain mystique to people who fight fires."
"The reason, Goldin said, lies with the mystique of the card."
"The far side of the moon has a certain mystique about it."
"The costs that the masculine mystique imposes are not just monetary." 
"It was an asset when computers were surrounded by mystique and controlled from the data processing department." 

Just the facts:

MYSTIQUE Definition & Meaning - Merriam-Webster

MYSTIQUE Synonyms: 42 Similar Words | Merriam-Webster Thesaurus