Lexical set

A lexical set is a group of words which share a similar phonetic feature. The lexical set says nothing about the specific realisation of its feature (its exact pronunciation), only that all the words in that set will have more or less the same pronunciation for that feature.

Use in English
One common use of lexical sets is for vowel categories or equivalence classes in the English language. Throughout the phonological history of the English language, there have been numerous splits and mergers, with the result that various accents and dialects make different distinctions between vowels. For example, some speakers of English pronounce luck and look identically, while others pronounce look and Luke identically, while still others distinguish between all three of luck, look, Luke. It is not possible, therefore, to say that, for example, sound A in dialect X corresponds to sound B in dialect Y.

However, it is possible to identify a number of lexical sets: groups of words which will have the same vowel sound in all or most varieties of English, and use these to talk about, for example, the specific pronunciation of the vowel characterising a particular lexical set in a particular variety of English.

In the example above, the words luck, look, Luke belong the lexical sets STRUT, FOOT, GOOSE, respectively. A common convention is to choose a particular keyword which is part of the set and to use this word, in upper case, to identify the entire set.

Lexical sets mean, for example, that people pronounce words in FOOT (such as good, full, bush) with the same vowel -- they do not say whether or not this vowel is distinct from that of, say, luck or Luke. In other words, lexical sets are intended to convey all distinctions that occur in the varieties of English under consideration, regardless of whether all those distinctions are present in any particular variety.

Standard lexical sets for English
A common set of 24 lexical sets, which covers a fairly wide range of varieties of the English language, is the Standard Lexical Sets described by John C. Wells in Accents of English.

These sets are as follows (in each case with the name of the set in uppercase letters and a few example words belonging to the set):

Note that not all varieties of English are covered by this collection of lexical sets; for example, varieties which distinguish wait from weight or those which distinguish nose from knows do not have separate lexical sets corresponding to these distinctions.