At any one time in a language certain words are transparent in their composition or in the derivational process used to construct them. A simple example can be offered with the word asleep which derives from Old English on slæpe but which in Modern English is not understood as being ‘on sleep’. In Old English what one had was a transparent phrase, in Modern English one has an opaque compound. In the framework of the present discussion one says that the phrase became lexicalised, i.e. speakers can no longer derive it from on + sleep but learn it as a single indivisible word.
Lexicalisation is most often connected with phonetic developments. Consider the following example. The word pan has full stress as it is a monosyllable, /pæn/. However saucepan has reduced stress on the second syllable so that the word is no longer interpreted as being ‘a pan for cooking a sauce in’. Nowadays the conceptual difference between the two words is that a pan is flat and broad (with a single long handle) whereas a saucepan is considerably deeper (usually with two short handles). One can say that saucepan is lexicalised, i.e. it is a single word and not derived productively from sauce + pan by native speakers of English nowadays.
Names frequently show lexicalised elements, e.g. Clapham, Greenham which contain as second element the Old English word hām ‘home’ which, because unstressed, did not undergo the later vowel shifts from /ɑ:/ to /əʊ/. This situation is also to be seen with the word hamlet ‘small village’ which now has a short /æ/ from Old English /ɑ:/ which was raised to /o:/ and diphthongised in Early Modern English to /əʊ/ in RP, yielding home /həʊm/. The result is that speakers no longer see a connection between home and hamlet and the latter word is lexicalised. Another instance of such lexicalisation is Lambeth which contains the words for lamb + heath but where the latter is reduced to an unstressed vowel whereas the independent word heath retained the long vowel and went through all later vowel changes.
Examining common words from the core vocabulary of a language shows that lexicalisation is a frequent process. For instance the words husband (a Norse loan) and woman are now indivisible forms but they each derive from two units, i.e. hus + bond ‘house’ + ‘servant’ and wīf + mann ‘female’ + ‘man’ respectively. Further instances which involve the shortening and reduction of vowels and which have led to a dissociation between the compound and its elements are holiday < holy + day; garlic < gar + lēc ‘sharp leek’; breakfast < break + fast; gospel < gōd spel ‘the good news’; sheriff < shire + reeve ‘county warden’.
Brinton, Laurel and Elizabeth Closs Traugott 2005. Lexicalization and Language Change. Cambridge: University Press.
Hickey, Raymond (ed.) 2003. Motives for language change. Cambridge: University Press.