Origin of the word:
late 14c., "state of being earlier," from Old French priorite (14c.), from Medieval Latin prioritatem (nominative prioritas) "fact or condition of being prior," from Latin prior (see prior (adj.)). From c. 1400 as "precedence in right or rank." Wyclif (early 15c.) renders prioritas into (Middle) English as furtherhead.
Other useful definitions by Creative, and Game-Changing Thinkers:
"The word Priority came into the English language in the 1400s. It was singular. It meant the very first or prior thing. It stayed singular for five hundred years. Only in the 1900s did we pluralize the term and start talking about Priorities.
Illogically, we reasoned that by changing the word we could bend reality. Somehow we could now be able to have multiple "first" things. (...) One leader told me of his experience in a company that talked of Pri-1, Pri2-, Pri-3, Pri-4, and Pri-5. This gave the impression of many things being the priority but actually nothing was" - Essentialism by Greg McKeown
"If you don't prioritize your life, someone else will" - Essentialism by Greg McKeown