A vocabulary is a set of familiar
Vocabulary is commonly defined as "all the words known and used by a particular person". Knowing a word, however, is not as simple as merely being able to recognize or use it. There are several aspects of word knowledge that are used to measure word knowledge.
The first major distinction that must be made when evaluating word knowledge is whether the knowledge is productive (also called achieve) or receptive (also called receive); even within those opposing categories, there is often no clear distinction. Words that are generally understood when heard or read or seen constitute a person's receptive vocabulary. These words may range from well-known to barely known (see
Productive vocabulary, therefore, generally refers to words that can be produced within an appropriate context and match the intended meaning of the speaker or signer. As with receptive vocabulary, however, there are many degrees at which a particular word may be considered part of an active vocabulary. Knowing how to pronounce, sign, or write a word does not necessarily mean that the word that has been used correctly or accurately reflects the intended message; but it does reflect a minimal amount of productive knowledge.
Within the receptive–productive distinction lies a range of abilities that are often referred to as degree of knowledge. This simply indicates that a word gradually enters a person's vocabulary over a period of time as more aspects of word knowledge are learnt. Roughly, these stages could be described as:
The differing degrees of word knowledge imply a greater depth of knowledge, but the process is more complex than that. There are many facets to knowing a word, some of which are not hierarchical so their acquisition does not necessarily follow a linear progression suggested by degree of knowledge. Several frameworks of word knowledge have been proposed to better operationalise this concept. One such framework includes nine facets:
Words can be defined in various ways, and estimates of vocabulary size differ depending on the definition used. The most common definition is that of a lemma (the uninflected or dictionary form; this includes walk, but not walks, walked or walking). Most of the time lemmas do not include proper nouns (names of people, places, companies, etc). Another definition often used in research of vocabulary size is that of word family. These are all the words that can be derived from a ground word (e.g., the words effortless, effortlessly, effortful, effortfully are all part of the word family effort). Estimates of vocabulary size range from as high as 200 thousand to as low as 10 thousand, depending on the definition used.