The word "narcissist" comes from the Greek myth of Narcissus, a beautiful young man who was so captivated by his own reflection in a pool of water that he could not look away, ultimately leading to his demise or transformation into the narcissus flower.  The story of Narcissus was popularized by the Roman poet Ovid in his work "Metamorphoses".  The terms "narcissism" and "narcissist" were later adopted by psychologists, like Sigmund Freud and Havelock Ellis, to describe the pathological self-absorption and excessive self-centeredness that the myth's central figure embodied. 

According to the Oxford English Dictionary (OED) the noun "narcissist" was first used in English in the 1910s,  with the earliest evidence dated to 1917 in the Journal of Philosophy, Psychology & Scientific Methods.  Narcissist was formed as a derivative of the term "narcissism", which itself was coined by British physician Havelock Ellis in 1898 to describe pathological self-absorption, or a mental illness.  The term "narcissism" was independently used in German as Narzissismus by psychiatrist Paul Nacke in 1899.  Sigmund Freud also adopted the term in 1910, expanding its use in psychological circles. 

Examples of "narcissist" used in a sentence: 
"She's a narcissist, striving to impress her tawdry wannabe high-brow friends." 
"The truth is, I generally just focus in on myself, the narcissist that I am." 
"Anyone could see it was more than a man, especially a narcissist, could take." 
"A narcissist of that magnitude could not resist parading his phiz on television." 
"The narcissist objectifies people and treats them as mere instruments of gratification." 
"The city's deputy mayor dismissed the activists as "narcissists" and insisted the wedding was the "high-quality tourism" Venice needs."