Heroic Couplet, figure of literature

A pair of iambic pentameter verse lines which rhyme to each of these lines consists of five iambic feet. In other words, each line consists of five pairs of syllables and in each pair the first syllable is unstressed. Such five feet arranged in a verse line are called iambic pentameter lines and with similar sounds, they are called heroic couplet. This verse forms was first introduced into English poetry by Geoffrey Chaucer.

Metonomy in English Literature

Greek word "Metonomy" means "a change of name". In metonomy the name of one thing is substituted for that of another with which it is closely associated. The association of one thing with another is so deep that whenever we think of one thing we can remember, the other which is substituted by former. For example-
"The crown is used to mean monarchy or when we think of the 'pen' we think of the writer. Thus 'Fear not' we are loyal to the throne".
In these sentences the throne is not physically a part of the king, the idea of kingship is closely associated and throne is used as the substituted of the king. So it is the metonomy.

Symbol in English Literature

A symbol is something which represents something else, often an idea or quality, by analogy. It may be conventional, private or extended. White, Lion, and rose commonly symbolize innocence, courage, and beauty. Such symbols exist by convention and tradition. A snake may stand for evil or wisdom, according to different conventions. Writers either use these conventional symbols or invent their own which are private symbols. Blake and Shelley, use both conventional and private symbols in their poetry. However, novelists also use symbols.

A symbol may be seen as a species of metaphor in which the exact subject is not explicit and may even be mysterious. A whole poem may be a symbol of this kind. Blake's The Stick Rose" is typical. Blake's children in his poems are symbol of innocence, Shelley's "West Wind" is a symbol of destroyer and preserver.