Among the ʻfigures of speechʼ recognized in rhetorical theory are a number of related figures having to do with verbal transference of various kinds. The general term for these is METAPHOR.
- Halliday (1985), Pag. 319

Metaphor is usually described as variation in the use of words: a word is said to be used with a transferred meaning. Here however we are looking at it from the other end, asking not “how is this word used?” but “how is this meaning expressed?”. A meaning may be realized by a selection of words that is different from that which is in some sense typical or unmarked. From this end, metaphor is variation in the expression of meanings.
- Halliday (1985), Pag. 320

The term ʻmetaphorʼ is also used in a more specific sense to refer to just one kind, in contrast to METONIMY; and sometimes a third term is introduced, namely SYNECDOCHE. All three involve a ʻnon-literalʼ use of words [...] Thus metaphor, metonymy and synecdoche are forms of lexical variation stemming from the three fundamental semantic relationships of elaboration, extension and enhancement [...].
- Halliday (1985), Pag. 319-320