Quite a few web resources claims that sister is an antonyms to word brother. I can agree with this in some way, but how correctly it is. So let say “relative” is synonymous for word brother. In the same time “relative” is synonymous for word sister. It seems like sister and brother in this sense are synonymous. Sure, if we take into account just sex (gender) it’s opposite things. But it looks like depends on perspective relationship between two words mentioned above can be either synonymous or antonyms, which is becoming really confusing.

Appreciate if someone shed a light on it.

  • 5
    How is 'relative' a synonym for 'brother'? A brother is one type of relative.
    – Davo
    Jun 18, 2019 at 13:39
  • 6
    There are all kinds of opposites. Is the opposite of a square a circle or is the opposite or a two dimensional shape a line? Pick a framework and work within it. Pick a different framework and get a different result.
    – Jim
    Jun 18, 2019 at 13:44
  • 4
    "Relative" is actually a hypernym to "brother"
    – wrymug
    Jun 18, 2019 at 13:50
  • 1
    Synonymy doesn't have a necessarily transitive relationship. Just because A is similar to B and B is similar to C that doesn't mean that A is similar to C. Jun 18, 2019 at 14:59
  • 2
    If "relative" is a synonym for "brother" (which I don't entirely accept) then the antonym is "unrelated person". I can't think of a single word for a person like that, the nearest is "stranger" but that doesn't cover unrelated friends, neighbours and acquaintences.
    – BoldBen
    Jun 18, 2019 at 17:17

1 Answer 1


A true antonym is a word opposite in meaning.

A brother and a sister are both relatives, or siblings, so I agree that in the context of discussing relatives they are not really opposite in meaning any more than cousin is the opposite of uncle - they are simply different relatives.

However, "brother and sister", like "male and female" are traditionally binary choices or binary options, meaning that if something is not one, then by default it must be the other. If you have a sibling it is either a brother or a sister (this is of course barring any modern view on the number of genders and I ask that if you feel strongly about that matter you do not allow it to cloud your view of how a question about English should be answered).

So, given a choice of two things, where it can only be one or the other, the two are technically opposites and therefore antonyms.

For example, "up" is obviously the opposite of "down". However, there are other directions such as left and right. They all have contrary meanings, but directionally there is an opposite relationship between left and right, and between up and down, reducing the 4 directions to two binary choices and two sets of anyonyms.

I would have to agree with the dictionary definition that "brother" and "sister" are antonyms when considering the (traditionally recognised) gender of siblings.

  • Let's hope neither the brother nor the sister has a sex-change. There will be a point in time when.... Jun 22, 2019 at 14:30
  • @edwinashworth That would only prove my point. If by a sex change you can go from being someone's brother to being their sister then the two are clearly opposite.
    – Astralbee
    Jun 22, 2019 at 19:20
  • The changeover point is either neither or both, a third possible state. // But of course you're right in that the terms 'opposite' and 'antonym' are often used loosely, with the problem that people ask questions based on the misconception that they're well-defined. Jun 23, 2019 at 12:52

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