[...] a group is in some respects equivalent to a WORD COMPLEX – that is, a combination of words built up on the basis of a particular logical relation. This is why it is called a GROUP (= ʻgroup of wordsʼ).
- Halliday (1985), Pag. 159

[...] A group – verbal group, adverbial group, nominal group – could be interpreted as a WORD COMPLEX: that is to say, a Head word together with other words that modify it. This is why the term GROUP came to be used. It means ʻgroup of wordsʼ, or ʻword groupʼ; and it suggests how the group no doubt evolved, by expansion outwards from word.
- Halliday (1985), Pag. 192