Knowing a word is not simple. First of all, learning a word involves learning more than just the word itself. A new vocabulary item may consist of more than just one word, for example, ‘post office’ and ‘mother-in-law’. From the point of view of word-formation, a word may be in the form of a single morpheme or it may be in the form of more than one morpheme with different bound or even compound words with more than one root but having only one identity such as ‘air-conditioning’. In addition, there are multi-word units such as phrasal verbs, compound words as well as idioms and metaphors.

However, just knowing the form of a word is not enough as we may find that students who know the formation of a word or a compound word may not necessarily know the meaning of its context. According to Hedge, vocabulary learning involves at least two aspects of meaning. The first aspect involves the understanding of its denotative and connotative meaning. The second aspect involves understanding the sense relations among words.