Back in my heyday, we’ve heard our fathers so often begin some boast of long-lost glory. The heyday of the train, the heyday of radio, the heyday of the flip-phone – each of these remembers some technological golden age of yore. Perhaps you’ve wondered: What is the hey– in heyday? As it turns out, we’re questioning the wrong part of the word.
Heyday
In the late 16th century, heyday named a “state of exaltation and excitement,” as the Oxford English Dictionary (OED) defines it. Shakespeare gets one of the earliest citations, as he is wont. When Hamlet confronts his mother with a picture of his late father, he says:
You cannot call it love, for at your age
The heyday in the blood is tame, it’s humble…
With “heyday in the blood,” Hamlet is referring to libido.
By the 18th century, heyday had shifted to “the stage at which excitement is at its height.” Here, the OED first quotes Scottish author Tobias Smollett’s 1751 (and fabulously titled) novel, The Adventures of Peregrine Pickle. Smollett uses heyday of his swaggering protagonist three times: “in the heyday of his gallantry,” “our imperious youth, in the heyday of his blood, flushed with the consciousness of his own qualifications,” and “in the heyday of his fortune.” In these instances, we can see heyday coming into its own semantic heyday: “the period of someone or something’s greatest vigor, popularity, strength, prosperity, or success,” especially used in the expression the heyday of youth.
Associations with the word day helped propel heyday from a “state of excitement” to “the stage at which something or someone is at their prime.” Day, of course, evokes time, and hey, additionally, may have called up high.
But etymologically, it seems there’s no day about it. The exact origins of heyday are unknown, but earlier in the 16th century, the record shows people shouting Heyda!, an exclamation of cheer, joy, or surprise. At the root of this playful cry is our Hey!, documented as Hei! in Middle English, though surely an older and organic vocalization. The -da in heyday eludes explanation, though for what it’s worth, German does have heida for “Hey there!”
The original -da, I suspect, is just one of those sounds or noises we hollering humans make. Heyda!
Mashed Radish 
It’s interesting to see the etymology of a word like this. It just goes to show language is an ever changing mishmash of symbols. Come to think of it now I’m wondering about the etymology of “mishmash”. Ha, it seems like one of those words that might have an interesting story.
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“An ever-changing mishmash of symbols”: I love that, and think it’s true! As for “mishmash,” it’s likely an imitative reduplication of “mash,” related to the word “mix.”
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