Behest is from a Germanic base meaning ‘bid’; related to hight.  Behest came to Old English behǣs ‘a vow'. 

The word "behest" first appeared in English during the Middle English period around 1200.  It originally meant "promise" or "pledge," derived from the Old English word "behǣs," which in turn came from "behatan" meaning "to promise". Over time, the word's meaning evolved to encompass "command" or "injunction," influenced by the related word "hest" (meaning "command").  The word's root lies in the Old English "behǣs," meaning "vow" or "promise," from the verb "behatan" (to promise).  Today, "behest" is most commonly used to mean an authoritative command or request, often in the phrase "at the behest of...".  A behest is a strong command or exhortation, often given by someone in a position of authority.  A request is a polite way of asking something. 

Examples of behest in a sentence: 
"At the behest of her friends, she read the poem aloud." 
"The meeting was called at the senator's behest." 
"The committee had assembled at the behest of the chairman." 
"The slaughter of all male infants under the age of two was done at the behest of Herod."
"He was merely rebalancing his portfolio, at the behest of his financial advisor." 
"I only made the change at the author's behest."
"Later in the episode, Mysaria was murdered by Larys (Matthew Needham) in a fire at the behest of the queen."
"The Senate didn't pay the $155 per diem to Clark for that meeting at the behest of Senate leaders."

Just the facts:

BEHEST Definition & Meaning - Merriam-Webster