Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

[Q]: In math, we use the term series a lot, and there are many types of series. How should I craft my sentence when I have three different ones in mind to talk about? Should I settle down for a less mortal alternative of 'list of series' or something like that? The existing question on The possessive and plural forms of 'series' suggests the usage of series'. But is that all? If that's the only solution, then could you please explain the usage of apostrophe symbol at the end? Is that a plural marker or a possessive marker, or both?.
[A]: Series (like deer, salmon, and sheep) is pronounced and spelled the same in the plural as in the singular. If either the singular or the plural is used as a possessive, an apostrophe is added to show that in print, though there is no pronunciation difference in speech. Thus, The series doesn't converge. (singular) The series don't converge. (plural) This series' limit is unknown. (singular possessive) These series' limits are unknown. (plural possessive) More examples can be seen here.

[Q]: This came up recently on programmers.SE, when someone (a Russian, presumably non-native English speaker) asked why we used the term 'sister sites', instead of 'brother sites'. Of course, I'm a native English speaker, and I have no idea either, hence this question. The full question, for context, was 'Several of our sister sites have taken to featuring Questions [...]'. It does seem odd, considering that English (usually) uses masculine terms as the default.
[A]: I suspect the terminology sister sites is derived from sister cities. Traditionally, cities, countries, and ships have been personified as feminine in English, although this is growing less common due to the influence of women's rights.

[Q]: I am looking for a list of all English words that are their own antonyms. Off the top of my head, I can only think of 'either', 'fast', 'to dust' and 'to lease', but there must be dozens more. Can you provide a link to a comprehensive list, if such exists? Also, what are such words most commonly called? I like the term 'Janus word' I once heard, but is that widely understood? Edited by popular demand to make it absolutely clear that this is not a community wiki poll.
[A]:
I think you're referring to Auto-antonyms. They are not the same word but a homograph (a word of the same spelling) that is also an antonym. I guess, Janus word is also acceptable. There was a list on Wikipedia (List of Auto-antonyms in English), since moved to Wiktionary's Appendix of English contranyms.