According to Ngram, anyway.

The vast majority of English speakers seem to have no idea what the word means.

Now why is that?

UPDATE: After reading some of the responses:

As a noun.

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    Words become obsolete all the time, and I can't imagine that coeval was ever le mot du jour. – Mick Jul 27 '19 at 22:49
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    How is this question not just "primarily" but wholly opinion-based? (I haven't closed it unilaterally because I appreciate that there may be an answer to this supplementary question.) – Andrew Leach Jul 27 '19 at 23:15
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    @AndrewLeach: Have you seen the overall quality of the questions posed here over the past year or so? Goodness gracious. – Ricky Jul 28 '19 at 0:53
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    @HotLicks Just like when you read primeval you think pre-evaluate, and when you read medieval you think mid-evaluate. Makes sense. – tchrist Jul 28 '19 at 1:57
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    How is it possible that a question can attract so many responses, yet still have no upticks? Mysterious. – Cascabel Jul 28 '19 at 2:08

In Search of Lost Etymons: Stalking Cranberry Morphemes

The learnèd word coeval, sometimes written coëval and formerly spelled coaeval or coæval, has fallen on hard times for one simple reason alone. Now that the clerical class is no longer required to study Latin, the constituent morphemes of the word are no longer accessible to them.

Because they no longer immediately know that eval meaning “of an age” is from Latin aevum, neither do they know what coeval means, and so it falls quickly into the forgotten desuetude all such cranberry morphemes (quick! what does cran- mean?) are destined to die in.

The same fate has befallen aeviternal, longaeval/longeval and even primaeval/primeval, and even mediaeval and mid-eval have become simply medieval with no one having any idea why in the world we refer to the Middles Ages as “medieval”.

In short, the illatinate masses cannot automatically recover the aevus or aevum portion of these words that gave them life and meaning. To anyone with any Latin, however, all these words have an obvious meaning related to a certain age, just as aeon does. Notice when each of these words entered in English, per the OED:

  • aeon, eon, n. (1581)
  • aeviternal, adj. (1596)
  • aeviternity, n. (1596)
  • aevum, n. (1660)
  • eval, adj. (1791)

  • coeval, adj. and n. (1605)

  • coevality, n. (1644)
  • coevally, adv. (a1711)
  • coeve, adj. (1659)
  • coevity, n. (1641)

  • longeval, adj. (1598)

  • longeve, adj. (1678)
  • longevity, n. (1569)
  • longevous, adj. (1652)

  • primeval, adj. and n. (1653)

  • primeve, n. and adj. (1619)
  • primevity, n. (1610)

In comparison, medieval from medium aevum is a recent borrowing that barely showed up 200 years ago, some 200 years after those in the previous set. Back then the educated still studied Latin and Greek, so its meaning was still apparent to them. Today, they do not, and so the connections have been lost.

Interestingly, the far more commonly used word age ultimately derives from the same Latin roots as all these words do, namely aevum and aevitas, but it has suffered the gnawing erosions [sic] of time until it is no longer recognizable as such.

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    This makes good sense. I don't suppose it can be easily 'proved' to a moderator's satisfaction, but it seems likely to me that coeval is replaced more often by 'at the same time as' than by 'contemporaneous'. – Dan Jul 28 '19 at 10:19

Coeval is a useful word with a straight-forward meaning. Yet I have never used it.

I realise that I say contemporaneous when I might as easily say coeval. Ngrams suggests that this is because contemporaneous replaced coeval around 1840!

Why did coeval fall out of favour? It is attractively short but, possibly, a more daunting pronunciation challenge....?

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  • A reason for the downvote would be interesting. – Dan Jul 27 '19 at 23:37
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    I upvoted on the strength of your having raised the possibility that the emergence of "contemporaneous" may have contributed to the demise of "coeval." I'm not sold on the one-for-one replacement theory, however. Meanwhile, "contemporaneous" has had to deal with its own challenge in recent decades: the rise in usage of "contemporary" ... – Sven Yargs Jul 27 '19 at 23:44
  • ... including at least some instances where the evident meaning of "contemporary" is "then-current" rather than "now-current." – Sven Yargs Jul 27 '19 at 23:44
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    Downvote... possibly because you have only answered the question with "I can't say why" (since edited out) or with a question mark (currently) but no substantive and corroborated answer. – Andrew Leach Jul 27 '19 at 23:50
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    @SvenYargs Back when it was impossible for an educated literate person to somehow manage to be illatinate, coëval’s meaning was clear. Once that stopped being impossible, all direct loanwords from Latin like this one became far more bewildering and befuddling than their Germanic brethren—however wild and fuddled. :) – tchrist Jul 28 '19 at 1:47

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