"a promotional advertisement," 1958 (in Billboard magazine headlines), shortening of promotion in the sense "advertising, publicity."
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promotion n.
c. 1400, promocioun, "advancement in rank, honor, or position," from Old French promocion "election, promotion" (14c., Modern French promotion) and directly from Latin promotionem (nominative promotio) "advancement, a moving forward," noun of action from past-participle stem of promovere "move forward, advance" (see promote).
From early 15c. as "advancement of a cause; assistance, help, support, encouragement." The meaning "advertising, publicity" first recorded 1925.