Mathwords

Mathwords provides easily-to-locate, formal definitions for about 2000 mathematic terms including a few from physics, finance, and modeling. Most definitions contain multiple references to other terms plus either diagrams or examples, but fewer have textual explanations. About 20 terms are accompanied by a dynamic diagram from McGraw-Hill's Geometer's Sketchpad, and 36 terms populate the real-world application list. Terms can be accessed using four search methods: A to Z, full list, subject areas, or Google powered native-and-paid-web-sites search.

If you just need a little nudge to remember a concept or term you already knew and understood, Mathwords will be a helpful reference. If you don't already have a really strong foundation, it could be quite frustrating. It seems like kids who can easily understand these definitions wouldn't need to look them up here in the first place. For example, multiple careful readings of the interrelated terms accuracy, precise, and significant digits built some understanding but raised unanswered questions as well. A comparison of two definitions of function, the first from the Common Core Standards, demonstrates the problems inherent in Mathwords's formal and reference-laden approach.

Common Core: "A function is a rule that assigns to each input exactly one output. The graph of a function is the set of ordered pairs consisting of an input and the corresponding output."

Mathwords: "function: A relation for which each element of the domain corresponds to exactly one element of the range."

You have to look up four other words to understand Mathwords' definition, which is a lot of work. Even with this formal approach intact, expanded definitions with better examples and diagrams would improve learning significantly.