"Knowing" a word means :
a) understanding its basic meaning (denotation) and also any evaluative or associated meaning it has (connotation). For example cottage and hovel are both types of small houses. But cottage suggests cosiness, a pretty house with a garden, probably in the countryside, whereas hovel suggests a run-down construction, dirt and squalid poverty. Many words have similar positive or negative connotations - consider slim and scrawny - and, in certain cases these connotations may lead to their being considered "politically incorrect" - for example handicapped.
b) understanding the grammatical form of the word and its syntactic use (colligation). For example, interesting, main and alone are all adjectives. However, while interesting (like most adjectives) can be either attributive or predicative - eg:
- It was an interesting discussion (attributive)
- The discussion was interesting (predicative)
c) understanding that words may have more than one meaning - eg boom may mean a loud sound, an increase in business, a pole to which a sail (on a boat) or a microphone or camera (in a TV or film studio) may be attached, or a heavy chain stretched across a river to stop things passing. Changes in meaning may also involve changes in colligation. To go back to the example of adjectives above, take the adjective old. With the meaning of aged it can be both attributive or predicative - We live in an old house / Our house is old. But with the meaning known for a long time it is only attributive - an old friend, an old saying. Using it predicatively -My friend is old - changes the meaning back to aged.
d) understanding that in changing meaning the word may also change form - eg fast can be an adjective or adverb meaning quick(ly) or a verb or noun related to a period of voluntarily going without food.
e) understanding what variety of English the word belongs to :
- is it informal, neutral or formal? Eg nosh - food - comestibles
- does it belong to a specific regional variety of the language (eg bairn in Scottish English), or does it have different meanings in different varieties of English? For example, biscuit in US and UK English.
- is it considered vulgar or taboo? Eg bollocks, asshole, shit
- is it an "everyday" term or a technical term and if the latter in what field? Eg feelers vs antennae in biology
- is it used in current English or is it archaic? Eg betwixt, damsel, looking glass
g) understanding how affixes can change the form and meaning of the word - eg help, helpful, unhelpful, helpfully, helpless, helplessness etc
h) knowing how it relates to other words in lexical sets. This includes relationships such as:
- hyponymy - for example a car is member of the category vehicle and thus asociated with other members of that category : bus, coach, lorry, motorbike etc.
- meronymy - for example an arm is part of a body and as such is associated with other parts such as leg, hand, head, ear etc.
- synonymy - words with the same meaning - eg flower, bloom, blossom
- antonymy - opposites ; big-small, dead-alive, open-close etc.
j) knowing its use in fixed and semi-fixed lexical chunks, such as multiword verbs (eg run in run out of) collocations (the use of heavy in heavy rain), idioms (to get cold feet), binomials (trial and error), and other types of figurative language which I discussed in detail here.
All this begs one important question however: are we talking about receptive understanding or productive use? Obviously, some features of the word - eg its basic denotation and possible connotations - are important for both, while colligation is perhaps only necessary for productive use. This will affect how we decide to teach the words, but so may other factors : what level are the learners? How can we teach lexis in such a way as to promote retention? Which other of the factors listed above should we take into consideration and how do we do it? These questions are discussed in various other articles - see the list under