About
Why this library exists
Most synonym pages hand you a list and leave you to guess which word belongs in your sentence. A list is not an answer. This is an attempt at the reference that should exist instead, one sense at a time.
A thesaurus is a machine for producing confident mistakes. Look up a word and you get twenty alternatives with no indication of which sense each one belongs to, so the chances of picking a word that means something adjacent to what you meant are excellent. The missing piece is always the same: which sentence are you in.
So the unit on this site is not a word, it is a word in a sense, and it never appears without a sentence. Every page names the true synonym for that sense, shows the sentence with the synonym dropped into the same slot, and then does the thing no list can do: names the closest wrong answer and explains what it actually means instead.
Where the bank came from
The foundation is Open English WordNet 2025, an open lexical database of English published under a Creative Commons Attribution licence. WordNet groups words into synsets, which is exactly the raw material a synonym game needs and exactly the wrong shape to ship as it stands: synsets contain rare variants, register mismatches and words nobody would offer a human as an answer.
So the bank was generated from it and then read. Every one of the 3,600+ surviving entries was checked by hand in July 2026: the sense gloss against the example sentence, the true synonym against both, and each of the three near misses against the test below. Entries that failed were cut, not softened. The result is smaller than the source and that is the point.
The fairness test
One question, asked of every entry: given only this sentence, is there exactly one defensible answer among the four tiles. If two tiles both work, the entry is unfair and no amount of good design fixes it. If the sentence would still make sense with the word removed, it is not doing its job and the entry needs a better one.
That test is why 1,900+ entries carry a written reason line. When a near miss is a real synonym of the base word in some other sense, saying so is more useful than marking the tile red. It is also the part of this library that has no equivalent on any thesaurus site we could find.
How it is organised
Two axes, both from the bank. 31 themes describe what a word is about, from qualities and actions down to weather. Five difficulty tiers describe how far up the mountain it sits, from Foothills at everyday vocabulary to Summit at the rare and formal end. Every word page links to both, and to a varied set of neighbours, so the library is walkable rather than searchable only.
Who publishes this
Synonym Stack is published by MomentumLab AI Pty Ltd, a small Australian software studio that builds and runs its own apps. There is no outside investor and no client work behind these pages. The game and the library are both ours, which is why the fairness rule could be enforced by deleting entries rather than by shipping them and hoping.
Getting in touch
Corrections are welcome and they get acted on. If a pairing on this site is wrong, or a sentence does not pin its sense down, tell us at admin@momentumlab.ai and it will be fixed in the bank, which fixes it in the app and on this site at the same time. Support questions are answered on the support page.
Read a word page before you trust a thesaurus again
Pick any word in the library. Two minutes with the sentence, the synonym and the reason will tell you more than a list of twenty alternatives ever did.