Are these words interchangeable? I'm especially interested in how formal/informal are they. Is there any difference between American and British usage?
The discussion on english-test.net where two native speakers argue about the word sibling inspired me to ask this question.
Best Answer
Sibling is more often used in American English when just referring to how many brothers and sisters a person has. Like "I have 5 siblings" or "Kelly has no siblings". This is more used on like surveys or questionnaires.. for whatever reasons.
In informal conversation, a sibling is used as a way to ask a person a question like "How many siblings do you have?" or "Do you have any siblings?". This is most often the sort of question that would be asked to get to know someone better. So with this type of question, the person normally would expect the answerer, to state how many are brothers and how many our sisters in their answer, not just the count of siblings. Like "I have 2 brothers and 3 sisters. Brothers are teenagers, one sister is graduated from college, and the other two sisters are in junior high school."