Definitions are a core part of any dictionary, and Wiktionary is no exception. Writing basic definitions requires some skill, more practice, and sometimes help.
There are a few basic guidelines to follow when writing a definition:
Numbering definitions: Each definition line should begin with a # (hash, octothorpe, pound sign). This will number the definitions. Place the hash at the leftmost position on the line, with no spaces or tabs prior to the hash. Additional definitions must be placed on a separate line, but there should be no blank lines within a group of definitions, since that will break the sequence of the numbering.
There are two basic styles of definition:
Most English entries follow the first style, so that their definitions should begin with a capital letter and end with a period. In other words, such definitions are formatted as if they were sentences, even if they are actually sentence fragments. In contrast, most non-English entries follow the second style, since they typically translate the non-English word to one (or a few) English terms. However, there are non-English terms defined in the first style, especially when the term has no simple or straightforward English translation, and so it must be explained fully rather than just translated. When translating a word with a single English term, you can use template {{gloss}} to disambiguate the used term.
Definitions with more than one explanation: When a definition consists of more than one parallel explanation, the parts may be separated by commas or by semicolons. Commas are preferred in separating short and simple items, but semicolons are preferred when separating longer defining phrases or clauses.
Linking: One of the more powerful tools at Wiktionary's disposal is the wikilink. Key terms in a definition should be linked by the use of double square brackets (i.e., ]) around the term. This creates a link to the entry for that term.
Links should always be present around any word in the definition that is synonymous, or nearly synonymous with the term being defined. Likewise, link words which provide key descriptions or qualifications in defining a term. However, do not link every word in a definition. Linking all the words detracts from the visual emphasis that a wikilink provides, and creates visual confusion. Articles, prepositions, conjunctions, particles, and other short words should never be linked unless they are synonyms or translations of the term being defined.
When the explanatory style of definition writing is used, special care must be taken to link the capitalized first word in the definition. Wiktionary is case sensitive, so a simple link of the first word will often yield a red (broken) link, or may link to a German noun that happens to be spelled the same way. In these cases, the link must be "piped", as in the example: ]. This links to the first (lower-case) word while displaying the second (capitalized) word.
The wording in a definition depends on the part of speech of the word being defined. Nouns, especially proper nouns, are considered the easiest, followed by adjectives, and verbs. The most difficult words are included in the other parts of speech, especially those with purely grammatical functions like prepositions, conjunctions, determiners, articles, and particles.
If a proper noun meets our standards for inclusion (WT:CFI), its definition should be relatively easy. If it seems to be difficult, insert a link to Wikipedia, follow the link to an article of that title if one exists or search for the term in other Wikipedia articles.
Concrete nouns are the next relatively easy class. Wikipedia may have an article. Wikicommons may have photographs or drawings. The insertion of photographs or drawings may reduce the need for users to rely on the words of a definition for the basics, allowing the definition to address questions of the boundaries of the term instead.
Abstract nouns are more challenging. Within this class the most challenging are core abstractions such as "time", basic emotions, etc. The easiest abstract nouns are those that are definable in terms of the most basic ones. Fortunately, few people will rely on a dictionary for the core abstractions. Definitions can be used to define the scope of the term, its boundaries, rather than attempting to define its essence.
Grammatical parts of speech include all conjunctions, pronouns, determiners, prepositions, articles and particles, and most of the most common adverbs. Such words are often very hard to define in the same way as nouns, verbs, adjectives, and most adverbs derived from adjectives. If a particular word of this type cannot readily be defined, for example, by a synonym, consider a "non-gloss definition". Such a definition would typically begin with words such as "Used to indicate ....". Such a definition needs usage examples or citations even more than other definitions do. To facilitate review of such challenging definitions, please put the definition inside {{non-gloss definition}}.
Interjections are not grammatical parts of speech, but also may not be easy to define. If a particular word of this type cannot readily be defined, for example, by a well-known synonym, consider a "non-gloss definition". Such a definition would typically begin with words such as "Used to express...", followed by a noun or noun phrase suggesting an emotion. Such a definition may need usage examples or citations even more than other definitions do. To facilitate review of such challenging definitions, please put the definition inside {{non-gloss definition}}.
See Wiktionary:Context labels for details on context/usage tags.