Origins
The word 'diction' entered English in the 1540s from Latin 'dictiō' (a saying, a word, an expression), derived from 'dictus,' the past participle of 'dīcere' (to say, to speak, to tell). The ultimate source is the PIE root *deyḱ-, meaning 'to show' or 'to point out,' which reveals the deep conceptual link between pointing and speaking that pervades Indo-European languages. To 'say' something was, at the earliest recoverable stage of the language family, to 'point it out' with words.
In English, 'diction' has two related but distinct meanings. The first, which appeared earliest, refers to the choice and arrangement of words in speech or writing — what rhetoricians call 'lexis.' A writer's diction may be formal or colloquial, Latinate or Anglo-Saxon, ornate or plain. The second meaning, which developed in the eighteenth century under the influence of elocution training, refers to the clarity and distinctness of a speaker's pronunciation — how well they articulate individual sounds and words. Both senses are united by the idea of words as the material of communication: in one case, which words you choose; in the other, how you produce them.
The Latin verb 'dīcere' generated one of the most extensive word families in English through its various derivatives. From the past participle 'dictus' came 'dictate' (to say repeatedly, to prescribe), 'dictator' (originally a Roman magistrate appointed to 'say' — that is, to declare — emergency measures), and 'diction' itself. From compounds of 'dīcere' came 'predict' (prae- + dīcere, to say before), 'contradict' (contrā + dīcere, to speak against), 'verdict' (vērum + dictum, a true saying), 'edict' (ē + dictum, something said out, a proclamation), 'indict' (originally 'indicāre,' to point out, later confused with 'dīcere'), 'benediction' (bene + dictiō, a well-saying, a blessing), and 'malediction' (male + dictiō, an ill-saying, a curse).
Latin Roots
The word 'dictionary' is itself derived from 'diction': it is, etymologically, a book of dictions — a collection of the words (dictiōnēs) of a language. The Medieval Latin term 'dictiōnārium' was coined in the thirteenth century by the English scholar John Garland as the title of a collection of Latin words organized by subject. The modern sense of an alphabetically arranged reference book of words with their definitions developed over the following centuries.
The PIE root *deyḱ- also produced Latin 'digitus' (finger — the pointing thing), 'docēre' (to teach — to show someone how), 'indicāre' (to point out), and 'index' (a pointer, a list). Through the Germanic branch, the same root yielded Old English 'tǣcan' (to show, to point out), which became Modern English 'teach,' and Old English 'tācen' (a sign, a mark), which became 'token.' The German word 'Dichtung' (poetry, literary composition), from Old High German 'tihtōn' (to compose), was borrowed from Latin 'dictāre' (to dictate, to compose) and shares this same deep root.
In literary criticism, diction is one of the fundamental elements of style analysis. Aristotle devoted a section of the Poetics to 'lexis' (diction), arguing that the poet's choice of words — whether ordinary, foreign, metaphorical, or ornamental — was essential to the effect of tragedy and epic. The eighteenth-century debate between 'poetic diction' (a special elevated vocabulary for poetry) and ordinary language anticipates the Romantic revolution: Wordsworth's Preface to the Lyrical Ballads (1800) explicitly rejected the idea of a special poetic diction, arguing that good poetry should use 'the real language of men.'
Spelling and Pronunciation
The word 'diction' in its pronunciation sense became central to English-speaking culture through the elocution movement of the eighteenth and nineteenth centuries, which emphasized clear, standard pronunciation as a mark of education and social status. This connection between diction and class remains potent — George Bernard Shaw's Pygmalion (1913), later adapted as My Fair Lady, is entirely built on the premise that diction defines social identity.