A kind of subordinate clause which does the work of an adjective. An adjective clause is used to modify a noun or a pronoun in the main clause.
An adjective clause is usually introduced by a relative pronoun or a relative adverb.
- This is the house that Jack built. (Here the adjective clause ‘that Jack built’ says something about the noun house.)
- The reason why I did it is obvious. (Here the adjective clause ‘why I did it’ says something about the noun reason.)
- People who are honest are trusted. (Adjective clause – who are honest)
- We love those who love us. (Adjective clause – who love us)
- The house where the accident occurred is nearby. (Adjective clause – where the accident occurred)
- All that glitters is not gold.
The relative pronoun or relative adverb introducing an adjective clause is sometimes understood, and not expressed.
- Where is the book I lend you? (= Where is the book that I lend you?)
- Eat all you can. (= Eat all that you can.)
A to-infinitive is sometimes used as an equivalent of an adjective clause.
- He has no clothes which he can wear. = He has no clothes to wear.
- I have got some work which I must do now. = I have got some work to do now.