Plural & Possessive Builder
Single words, hyphenated compounds, and multi-word titles all work — try “editor in chief”.
Type a noun and get all four forms it can take: the singular, the plural, the singular possessive, and the plural possessive. The four are worth seeing together because the mistakes people make are almost always mistakes about the relationship between them — writing "the sister's passports" when three sisters own them, or "the childrens' coats" for a plural that never ended in -s to begin with. Compound nouns are the reason this tool exists in the form it does. "Editor in chief" pluralises as "editors in chief", not "editor in chiefs", because the plural attaches to the noun naming the actual person rather than to the last word in the phrase, and no dictionary lookup of the whole phrase will tell you that. The builder handles hyphenated compounds, spaced compounds, and the post-positive titles English inherited from Norman French — attorneys general, courts martial, notaries public — as well as Latin and Greek plurals like addendum and addenda, criterion and criteria, analysis and analyses. Where this site already has a researched page for the noun you typed, the builder returns that published form and links you to it.
How it works
There are two sources of answers here, and the order between them is the whole design. The first is the site's own published research: two hundred and two nouns have their own entry, each one written and checked individually, and if you type one of those the builder returns exactly what that page says. A tool that quietly disagreed with the reference pages next to it would undermine both, so published data wins outright and the result carries a link to the page it came from. The second source is a rule engine, for the enormous majority of English nouns that no reference site has written a page about. It works down a chain of patterns in order of specificity. Zero plurals come first — sheep, deer, series, aircraft, where the form does not change at all. Then the Old English irregulars that changed their vowel instead of taking a suffix: man and men, foot and feet, mouse and mice. Then the classical borrowings, each restricted to a curated list rather than applied to every word with the right ending, because English is full of nouns that look Latin and are not: "album" ends in -um and its plural is "albums", so a blanket -um to -a rule would produce nonsense. Then the ordinary English patterns — a hissing or hushing sound at the end takes -es because a bare -s would be inaudible after it, a consonant before -y turns the y into -ies while a vowel leaves it alone, the handful of -f nouns that made the f-to-v shift take -ves while the ones that did not take -s. Compounds are handled before any of this, by finding the head noun first. A linking word — in, of, at, by, de — means the head is the word in front of it, which is why the plural of "editor in chief" lands on "editor" and the plural of "cul-de-sac" lands on "cul". A post-positive adjective — general, martial, public, laureate, apparent — means the same thing, because the adjective is sitting after its noun in a word order English borrowed and kept. When neither applies, the last word is the head and takes the plural, which is how "washing machine" becomes "washing machines". The possessives are then built from whichever plural came out. The singular possessive adds an apostrophe and an s. The plural possessive adds an apostrophe alone when the plural already ends in s, and an apostrophe plus s when it does not — which is the whole reason "children's" and "students'" look so different from each other. Compounds take their possessive at the very end of the phrase rather than on the head noun, so it is "editors-in-chief's decision", and the builder says so explicitly because it is the one part of the compound story that surprises people who have already learned the rest of it.
Where two forms are both correct
English has a real and unresolved split in several places, and a tool that picked a winner silently would be lying about the state of the language. Where two forms are genuinely accepted, both are shown. Latin borrowings are the largest group: formulas and formulae, indexes and indices, cactuses and cacti are all in use, and the classical form tends to hold in academic and technical writing while the anglicised form is normal everywhere else. Sometimes the two have quietly split by meaning rather than by register — indices in mathematics, indexes at the backs of books. The other split is the singular possessive of a name or noun already ending in s. Chicago style writes "James's" and "the boss's"; AP style writes "James'" and "the boss'". Neither is a mistake. The builder shows you both whenever the singular ends in s, and the only real rule is to pick one and hold it consistently through a document.
When the answer is a rule rather than a page
If the noun you typed has no entry on this site, the result says so. That is not a hedge for its own sake: a rule engine is applying a general pattern, and English keeps absorbing nouns that arrive with a plural of their own, so a pattern is exactly the kind of thing a recent borrowing or a proper noun can defeat. For everyday nouns the rules are reliable enough to trust. For anything unusual — a technical term, a brand name, a word borrowed in the last fifty years — the result is a good first answer and a dictionary is the second one. The tool tells you which situation you are in rather than presenting both with the same confidence.
Frequently asked questions
Why is it "editors in chief" and not "editor in chiefs"?
Because "editor" is the head of the phrase — the word naming the actual person — and "in chief" is a qualifier explaining which kind of editor. English pluralises the head, not the last word. The same logic gives you mothers-in-law, courts martial, and men of war. "Editor-in-chiefs" is increasingly heard and is shown as a secondary form, but edited writing still expects the first.
What is the plural of addendum?
Addenda. It is a Latin second-declension neuter noun, and that class forms its plural in -a rather than -s. "Addendums" appears in general writing and is not wrong enough to object to, but in legal, academic and publishing contexts addenda is the expected form. The same pattern gives curricula, memoranda, errata and referenda.
How do I write the possessive of a plural?
Look at how the plural ends. If it ends in s — dogs, students, editors — add an apostrophe only: dogs', students'. If it does not — children, women, people, sheep — add an apostrophe and an s: children's, women's. That single test covers every plural possessive in English, and it is why "childrens'" is always wrong: there is no such word as "childrens" for the apostrophe to follow.
Does it handle names and proper nouns?
It will produce forms for them, and the plural and possessive rules are the same ones that apply to common nouns. The place to be careful is a name ending in s, where the Chicago and AP conventions genuinely differ, and a name with an unusual origin whose plural may follow its source language rather than English.
Where do the published forms come from?
From this site's own plural pages, each of which was researched and written individually rather than generated. When the noun you type has one, the builder returns what that page says and links to it, so the tool and the reference layer can never drift apart into two different answers.
Is anything sent to a server?
No. The published-plural index and the rule engine both ship with the page, and everything is computed in your browser. The noun appears in the page address so the result can be linked and shared, and that address is only ever seen by anyone you choose to send it to.