Semantic stability within English idiomatic expressions

The aim of this thesis is to address a gap in historical semantics concerning idiomatic expressions by testing the hypothesis that an idiom can change its meaning over time while retaining its initial form. The linguistic literature so far has been focused on semantic change in words, on diachronic patterns according to which a lexeme changes, and on grammatical constructions that have gone through grammaticalization or lexicalization processes. This thesis presents a study of idiomatic expressions, where idiom is defined as a fixed multi-word expression with non-compositional meaning. A historical corpus of English within a period of 140 years has been designed that allows for the same idiom to be traced back and its usage contexts to be compared. Using diachronic methods similar to the ones used for the study of single words (e.g. frequency of co-occurrence, semantic fields, synonymous substitution), I have analysed 28 idioms in terms of semantic change. The findings show that idiomatic expressions are able to acquire additional meanings over time. I identified common patterns in the development of idiom meaning, and one of the common trajectories appears to be from a specific, narrow meaning towards more generalized, broader meaning and vice versa, often in relation with metaphorical and/or metonymical changes. The results indicate that the less opaque and fixed an idiom is, the more open it is to additional meanings. Further research would benefit from a wider time span and a bigger sample to incorporate more types of idiomatic expressions.