My best guess is that genethlical is related to the stars and their study and has some connection with astrology. Even Google can't give a proper definition.

  • 3
    Where did you find this word? Link? Give the sentence in which it appears plus a link.
    – Mitch
    May 8, 2018 at 23:07
  • genethliac(al)” seems to be more common
    – herisson
    May 8, 2018 at 23:08

2 Answers 2


The full-size Oxford English Dictionary (1971) does not include a separate entry for genethlical, but it does have entries for genethlic, genethliacal, and (the primary term) genethliac. Here is the OED's entry for the adjective form of this last word:

Genethliac a. and sb. Obs. Also genethliak, 7 -aque, -ake, 7–8, -ack. {Ultimately ad. Gr. γενεθλιακος belonging to one's birth or birthday (= γενεθλιος f. γενιθλη birth, breed, race, f. γεν- to bear, bring forth), whence late L. genethliac-us, F. généthliaque : from these the English forms are more immediately derived.} A. adj. Relating to the casting of nativities. Also, relating to a birthday. [Cited examples from 1616 through 1751 omitted.]

It follows that the phrase "genethlical astronomy" refers to astrology or horoscope casting—that is, to star- or constellation-based forecasting tied to one's birthdate. James Payn, Melibœus in London (1862) confirms this meaning:

Next door resided a genethlical astronomer. Meliboeus, who is proud of his acquaintance with the ancient classics, explained to me that this meant an astrologer ; and mighty convenient it must have been for any dramatic tyro, who had only to step around the corner to learn whether he was born to be "a star" or no.

(This excerpt also provides an interesting early instance of "a star" in the sense of "a theatrical sensation or matinee idol.")

Other early instances of genethlical in Google Books search results include a letter of October 14, 1793, from J. B. of Islington, published in The Astrologer's Magazine, and Philosophical Miscellany (1793) [combined snippets]:

As I shall send you, with a total indifference to names, whatever may be likely either to amuse or instruct the sidereal student, whether written by Gadbury, or Parker, or by Partridge, or any other of their adversaries, you will, no doubt, sometimes discover contradictions, and occasionally repetitions will unavoidably occur; yet I trust that the extracts I have selected will entertain your readers, familiarize the study of astrology, and to some such candid, inquisitive, and literate artist like Mercurius, furnish much useful matter to methodise and improve the genethlical art.

And from a letter dated March 10, 1812, from Plumsted, published in The Gentleman's Magazine (May 1812):

In a society I once belonged to, on an ill-natured dispute taking place about it [astrology], I proposed to investigate the genethlical part of this subject, by trying how far an aphorism relating to the eyes would hold good. It is said, the right eye of a man and the left eye of a woman the Sun rules, and the left eye of a man and right ye of a woman the Moon rules ; and when either of those bodies are in or near the meridian at the time of a person's birth, and are a few degrees Westward of Saturn or Mrs, the native will have a cast in the eye, which will incline inwards or towards the nose ; but if they have passed those bodies, and are a little to the Eastward, it will be outwards or from the nose. As far as I had opportunity of getting cases, this aphorism held good ; but, in order to show I was not mistaken, I proposed to have given me the period of births of twenty adult persons, one of which should have a remarkable defect in one eye, and the rest should have both eyes perfectly free from any such defect ; and if, by aphorism, I could point out the date of the defective person, and could repeat this as often as might be deemed needful for certainty ; I considered it would amount to a proof of the existence of Genethlical Astrology.

The upshot of all this is that genethlical is more precisely linked to birthdates than to stars, so it would seem to encompass numerological forms of birthdate-related augury as well as astrological forms; "genethlical astronomy (or astrology)," however, seems to refer more narrowly to the effects of planetary positions at one's birth on one's physiognomy and one's fate—and specifically on the casting of horoscopes on that basis and on the basis of the planets' subsequent positions.


Genethlical Astrology, from this and others:

The Guide to Astrology Containing a New and Complete System of Directions in Genethlical Astrology, Vol. II Amazon

genethliac collins noun

  1. Also: a genethliacon. a birthday poem.
  2. astrology a person who casts horoscopes. adjective also: genethliacal

Some choose to drop an "a"!

Used Rarely. genethliac is in the lower 50% of commonly used words in the Collins dictionary

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