Halliday & Matthiessen (1999: 194-5):
… there is no limit to the differentiation that may be drawn between one class of things and another; each of these very broad categories comprises numerous micro categories within which (as a glance at Roget's Thesaurus quickly reveals) relatively small sets of closely related things are grouped together. We naturally think of these as being semantic groupings, for which we can find general labels by moving a little way up in the taxonomy: parts of the body, household appliances, edible grains, spectator sports, emotional disorders, and so on, and so on. Such groupings are most readily presented as lists of words and word compounds; but they are not simply lexical, they are lexicogrammatical, displaying some characteristic combination of grammatical properties or preferences.