Does a dictionary need a glossary? It’s a moot point. Here are quick explanations of some terms used in OED Online, with links to more detailed discussion elsewhere.
Additions sections are used to append new senses and lemmas to unrevised entries from the Second Edition of the OED. Additions sections may come from the Additions volumes published between 1993 and 1997, or from the Third Edition revision project.
Each Additions section has a header showing where and when it was first published. You can see several Additions sections at the end of the entry for forward.
When an entry is revised for the Third Edition, any Additions sections are integrated into the main body.
A cited form is a word cited in an etymology: typically a foreign or early form of a word, cited as an antecedent or cognate of the word in English.
Cited forms are shown in italics. See, for example, mousseline, mussolina, and muselina in the etymology of muslin.
You can search for particular cited forms using Advanced Search.
A compound is a fixed term formed by combining two existing English words: usually an adjective and a noun (e.g. black hole), or a noun and a noun (e.g. rocket engine).
More significant compounds are treated as entries in their own right, especially if the compound has several meanings, or if it has a history distinct from that of its component parts. See, for example, parish pump.
A cross-reference is a reference from one point in the dictionary to another. In OED Online, cross-references are shown in blue, and act as hyperlinks: you can hover over the cross-reference to see the target definition, or you can click to go to the target.
External cross-references link from one entry to another; internal cross-references link from one point to another within the same entry.
Strictly, a derivative is any word which derives from another. In OED Online, the term is usually used to describe words which derive from other English words through regular processes of word-formation, such as the addition of -less to a noun to form an adjective: thus moonless is a derivative of moon.
There are three main editions of the OED (the Third Edition is not yet complete), and a number of supplementary publications. OED Online uses Third Edition entries as they are completed, and updated versions of the Second Edition entries: see About OED Online.
For a complete account of the OED‘s editorial history, see OED editions.
Entries are the primary building blocks of the dictionary. Each entry represents all the senses of a given headword, throughout its recorded history. The entry is structured to show the evolution of senses and uses over time.
The OED currently contains about 270,000 entries, although this number increases with each update.
The etymology is the section at the top of an entry (below the forms section) dealing with the origin and derivation of the word.
The ‘Forms’ section at the top of many entries (above the etymology) lists the variant spellings, with dates and labels indicating the periods and areas where each variant is found. The Forms section also lists irregular inflections, plurals, etc. For examples, see mammoth, offer, and worldly.
The headword is the main word at the top of an entry (shown in red in OED Online).
The form of the headword usually reflects the standard modern spelling of the word. Where there are two standard modern forms (e.g. British and U.S. spellings), the entry has dual headwords, separated by a vertical bar. See, for example, manoeuvre | maneuver. By convention, the British spelling is given first, and determines the order of the entry in the dictionary; but you can search for the entry using either spelling.
A homograph is a word with the same spelling as another, but of different origin and meaning. Homographs are treated as separate entries. They are distinguished by superscript numbers.
An example is the word lime, which in modern English can mean a chemical, a fruit, or a tree: these are three distinct words, etymologically unrelated to each other. The OED therefore treats them as three separate entries: lime, n.1, lime, n.2, and lime, n.3
The order of homographs is determined by date: the earliest homograph is listed first.
A lemma is any lexical item—a word, compound, phrase, or derivative—covered in a dictionary entry. In OED Online, the term is normally used to refer to lexical items contained within the body of an entry, as opposed to the entry headword.
Examples are preacher man, preacher-in-the-pulpit, and preacherdom (among others) in the entry for preacher.
The OED currently contains about 220,000 lemmas, in additions to the 270,000 main headwords.
If an entry, sense, or lemma is no longer in use in the English language, it may be considered obsolete. This usually means that no evidence for the term can be found in modern English. The latest quotation indicates the period when the term was last in use.
If an entry, sense or lemma is obsolete, this is indicated by the obelisk or ‘dagger’ symbol (†) and the label Obs.
A phrase is a multi-word expression regarded as a lexical item in its own right. Phrases are treated as lemmas under the appropriate entry.
An important subset of phrases are phrasal verbs. A phrasal verb consists of a verb and another element (typically an adverb or preposition) which together function as a single syntactical unit, as to break down, to make up, or to take out.
Significant phrases (especially phrasal verbs) are treated as subentries, and in some cases may have several senses of their own. See, for example, to melt away and to melt down under the entry for melt.
Most current (i.e. non-obsolete) entries include a pronunciation at the top of the entry. Some derivatives and other lemmas also have a pronunciation, where this may not be readily inferred from the headword.
Each pronunciation is shown inside a pair of forward-slashes (/…/). Pronunciations are given using the International Phonetic Alphabet.
The OED is based on quotation evidence: real examples of words in use, throughout the written record. Almost every sense and lemma of every entry includes a set of quotations showing when, where, and how it was used. The OED currently contains over 3 million quotations.
Each quotation includes a date, details of the source from which the quotation is taken (author, title, page number, etc.), as well as the quotation text itself.
OED Online enables you to search quotations discretely: see Choosing the scope of your search in the Help pages.
Each entry includes one or more senses. Each sense represents a distinct meaning of the headword. Significant lemmas are also treated as separate senses.
OED Online enables you to search senses discretely: see Choosing the scope of your search in the Help pages.
The OED currently contains about 800,000 senses, although this number increases with each update.
A subentry is a block containing a lemma, its definition, and its quotations. In the entry for preacher, the blocks containing preacher man, preacher-in-the-pulpit, and preacherdom (among others) are subentries.
In OED Online, subentries are functionally equivalent to senses. Searching or browsing by sense will include subentries as well as regular senses (see Choosing the scope of your search in the Help pages).
Variant spellings are listed in the forms section at the top of an entry. Variant spellings show all the ways in which a word has been written, over time and in different regions.
Where a variant spelling is particular to a certain use of a word, it may be listed at the appropriate sense; see, for example nonpareillo and nonparella at sense B.1.b of nonpareil.