Halliday & Matthiessen (1999: 286):
Almost all technical terms start out as grammatical metaphors; but they are grammatical metaphors which can no longer be unpacked When a wording becomes technicalised, a new meaning has been construed — almost always, in our present-day construction of knowledge, a new thing (participating entity); and the junction with any more congruent agnates is (more or less quickly) dissolved. If for example we said that engine failure had now become a technical term, what would we mean by this? We would mean that the semantic bond with a figure an/the engine fails had been ruptured (it could no longer be 'unpacked'); and that a new meaning, an abstract participating entity or thing 'engine failure' had come into being which had the full semantic freedom — to participate in figures, to admit of classes and properties, and the like.