This thesis combines a philosophical interpretation of Epicurean attitudes to language with literary analysis of the language of DRN. Chapters 1-2 describe Epicurean attitudes to diachronic and synchronic linguistic phenomena. In the first chapter I claim that the Epicurean account of the first stage of the development of language involves pre-rational humans acting under a ‘strong’ form of compulsion. The analogies with which Lucretius describes this process were motivated by a structural similarity between the Epicurean accounts of phylogenetic and ontogenetic psychology. Chapter 2 explores the Epicurean account of word use and recognition, central to which are ‘conceptions’. These are attitudes which express propositions; they are not mental images. Προλήψεις, a special class of conception, are self-evidently true basic beliefs about how objects in the world are categorized which, alongside the non-doxastic criteria of perceptions and feelings, play a foundational role in enquiry. Chapter 3 offers a reconstruction of an Epicurean theory of metaphor. Metaphor, for Epicureans, involves the subordination of additional conceptions to words to create secondary meanings. Secondary meanings are to be understood by referring back to primary meanings. Accordingly, Lucretius’ use of metaphor regularly involves the juxtaposition in the text of primary and secondary uses of terms. An account of conceptual metaphor in DRN is given in which the various conceptual domains from which Lucretius draws his metaphorical language are mapped and explored. Chapter 4 presents a new argument against ‘atomological’ readings of Lucretius’ atoms/letters analogies. Lucretian implicit etymologies involve the illustration, via juxtaposition, of language change across time. This is fully in keeping with the Epicurean account of language development. Chapter 5 describes Lucretius’ reflections on and interactions with the Greek language. I suggest that the study of lexical Hellenisms in DRN must be sensitive to the distinction between lexical borrowing and linguistic code-switching. I then give an account of morphological calquing in the poem, presenting it as a significant but overlooked strategy for Lucretian vocabulary-formation.