A Definition is a paraphrase, using one or several sentences, of the concept expressed by a given Expression. This Definition together with that Expression constitutes the DefinedMeaning. Various forms of the same word will be paired up with the same Definition to constitute their own DefinedMeaning in a manner not yet fixed.
The Definition may be translated into other Languages, and if this translated Definition can be adequately expressed by an Expression in the language in question, the pair of Definition - Expression may be seen as a DefinedMeaning as well for the purpose of translation to yet other languages. However, in case of doubt, the original Definition is leading.
If the Definition may not be adequately expressed, it may be approximated by an Expression, but should then be marked as not identical. This implies that the Expression used will need to be paired up with another Definition that does adequately paraphrase the concept it expresses to form another DefinedMeaning.
There is now basic support for providing an alternative wording for the same Definition. This alternative Definition should express the same concept as the original Definition, but worded for another intended audience; for example a more scientific description or a description suitable for children or second-language learners. It should not be used to express a slightly different concept, for that a second DefinedMeaning should be added.
 Guidelines for writing good Definitions
- Start Definitions with a capital letter and end complete sentences in a full stop/period or equivalent, depending on script.
- Be specific. When creating the Definition, take similar objects, phenomenon or activities into account. Does the Definition serve to differentiate between them?
- This is at a concept level, independent of any language. (Properties specific to expressions/languages are unavailable)
- Avoid using the associated Expression(s) in the Definition.
- Do not use "meta-expressions" such as the word or the expression. Other synonyms or translations might not be of the same type.
- If it is a species include the scientific name in the definition and add it as "International" Translation (Syntrans). Note: The first letter of the first name, the genus, is always capitalized, while that of the second is not.
- If it is a natural number, include the digit(s).
- Try to minimise the use of closely related and/or derived terms in the Definition, since this might easily lead to circular definitions such as wide being defined as having great width, and width being defined as the state of being wide.
- A dictionary is not an encyclopedia. The definition should concisely impart the meaning of an expression without giving extra information. You can provide a link to Wikipedia for access to further information.
 Translating Definitions
- Use the first Definition (unfortunately still unmarked) as source language for your translation if at all possible. If you do have to use another translated Definition as source, it is a good idea to indicate this in the summary field. In fact, until we have a clear marker of which is the first Definition, it might be a good idea to always include this information.
- Follow the source language as closely as possible while still creating good, grammatical sentences in the target language.
- A plain translation of a definition may be using a word which is ambiguous in the target language. If that cannot easily be avoided, add a disambiguation hint in brackets.
For Example, in English, you might want to write "similar to a big crank" rather as "similar to a big crank (the hardware item)" so as to avoid it being misinterpreted as referring to class of persons called cranks.
- A generic term like boat may refer to many narrower terms like fisherboats, row-boats, sailboats, riverboats, steamboats etc. These are not to be considered as translations, these can be found as narrower terms (hyponyms) in the relations.
- If a definition lists several narrower terms as samples (that is, followed by "etc." or "…") since the language lacks a broader, collective term, a translated definition may nevertheless use a collective term in the target language, if it is precise. Too wide, narrower, or foggy terms must be avoided!
 Format of the definition
The definition should be ideally a single sentence that is short and easily understandable. If you cannot translate an existing definition into your own language and keep the meaning in one sentence, try to break it up using semicolons or parentheses.
A definition should be written in a way that if it were substituted for the expression being defined, a sentence containing that expression would still make sense. For example, assuming that "car" can be defined as "[a] motorized vehicle with four wheels", you could substitute this definition for the word "car" in the sentence "he has a very fast car" and the new sentence would still make sense.
Some function words (or structural words) cannot be defined in the manner above. For example the word "and" is best defined in terms of its grammatical function: "a word used to separate the last word of a list from the other items of the list". This definition cannot be substituted meaningfully for the word "and" in a sentence such as "I need to buy milk, bread and sugar". In OmegaWiki such definitions are presented differently from the other "substitutive" type of definitions, they are shown inside square brackets:
- and: [A word used to separate the last word of a list from the other items of the list.]