"I do not say, Sancho," replied Don Quixote, "that it is imperative on knights-errant not to eat anything else but the fruits thou speakest of; only that their more usual diet must be those, and certain herbs they found in the fields which they knew and I know too."
Don Quixote laughed at the adaptation of the name, and the curate bestowed vast praise upon the worthy and honourable resolution he had made, and again offered to bear him company all the time that he could spare from his imperative duties.
There are no more uses of "imperative" in the book.
Show samples from other sources
I’m hoping to be able to reveal this to my father soon enough, but, for tonight, discretion is imperative."
Kiera Cass -- The One
The evolutionary imperative that drove them to live in groups was the opportunity to kill them by the billions.