The word "cryptid" originates from the combination of the Greek word "keypto" meaning "hide" or "hidden" and the English suffix "-id", which often denotes a member of a group or class. 

The earliest known use of the noun cryptid is in the 1980s. OED's earliest evidence for cryptid is from 1983, in the writing of J. E. Wall. a cryptozoologist, in a letter to the editor of the International Society of Cryptozoology's newsletter.

Examples of "cryptid" used in a sentence:
"A cryptid is a creature whose existence is rumored or reported but not proven by scientific evidence." 
"Slick was also devoted to adventure — and the search for cryptids."
"Lewis is killed in a car accident, Noah feels that the only person who can understand him is the famed cryptid Mothman." 
"You can only rule one individual case at a time as not being a cryptid." 
"The true definition of a cryptid is an animal that has not yet been classified by zoology." 
"It examines some of the legends and hypotheses surrounding this cryptid and also shows clips from other videos as well as drawings based on descriptions from "eyewitnesses". 
"Chupacabra, also known as Chupacabras, is a cryptid that is believed to be indigenous to Mexico, Puerto Rico, South America and the United States.