What could be a word for people who are born on the same day but are not siblings?

I am creating a website and matching my college students who were born on same day. I need an appropriate or the closest equivalent word in English to describe that situation. A word or short expression that I could use as its domain name.

I'm not expecting the exact word for this situation, but at the very least it should be an appropriate and acceptable one, even a short phrase will do but its meaning must be comprehensible to visitors to the website.

I need a single word or combination of two words that should be very catchy for the audience.

Can anyone help?

  • 2
    We were born on the same day.
    – WS2
    Jul 28, 2015 at 9:01
  • Statistically speaking, in a room of 30 people there is more than 50-50 chance that a least one pair were born on the same day. I can´t prove it but I just know it is true! Jun 24, 2017 at 22:49
  • @Cascabel There may well be more than a 50-50 chance that a pair of them HAVE THE SAME BIRTHDAY. However the OP here is talking about people born on the same day - quite a different thing. If the age distribution of the 30 were entirely random - from 0 to age 90 - then I calculate that there would only be approx. one chance in 75 that you would find two born on the same day. This should be on the maths or statistics site!
    – WS2
    Jan 15, 2020 at 23:14
  • @WS2 - 1 in 75 sounds high, but admittedly probability is weird, and of course as we all know million-to-one chances crop up 9 times out of 10.
    – nnnnnn
    Jan 16, 2020 at 1:04

5 Answers 5


I've heard the phrase "cosmic twin" be used for such folks. "Oh, your birthday is August 1, 1982? So is mine! We're cosmic twins!"


what about these suggestions?

"birthday twins" (born on the same day & same month)

"birthdate twins" (born on the same day & same month & same year)

"time twins" (born on the same day & same month & same year)

btw. there is a similar website with people born on the same day (same date) - https://birthdays.astro-seek.com

  • When I think of "twins," we automatically assume they had the same mother.
    – Steve
    Oct 29, 2021 at 17:40

My late mother-in-law used to call them "Fairy Twins"! I still use the expression now.


Mono-diurnal. is the answer you looking for. if you still are lol

  • 1
    Ha ha, Still this answer is relevant and helpful to me. I could not able to find a definition of explanation for your answer, If you add a reference and or a explanation will be really helpful Jan 16, 2020 at 2:46
  • 2
    Answers to word and phrase requests should be backed up with links to reputable dictionaries. In most cases it is helpful to quote the relevant definition here as well.
    – CJ Dennis
    Jan 16, 2020 at 9:09

You could call them "co-stars".

This would be catchy because it sounds as though they are movie stars.

It also hints at the fact that they were born under the same star-sign.

  • That would be a good one, But i am expecting little more word suggestions,So that in could get to a conclusion for the answer Jul 28, 2015 at 8:45
  • Too general. The question is about simultaneous dates, not star signs.
    – Anton
    Jul 28, 2015 at 8:55
  • @Anton - Thanks for the comment. I think it's a little harsh. Quote "I'm not expecting the exact word for this situation" and "two words that should be very catchy for the audience" - I did my best to fulfil both those requests. :-) Jul 28, 2015 at 8:59

Not the answer you're looking for? Browse other questions tagged or ask your own question.