Onomatopoeia (adjective onomatopoeic) is a figure of speech which uses words to imitate the sounds they are describing. Words like 'Boom!' and 'Crash' are everyday examples, as is the child's word for an ambulance, 'Nee-naw', trying to imitate the sound of its siren. Advertisers often appeal to onomatopoeia: "Snap, crackle, pop" is a slogan based on the sound of a cereal reacting to milk. Comic strips and graphic novels often invent new words to communicate the sounds of their scenes, often the violent sounds: 'Ker-pow!' and 'Zap' are examples.
Poets often use onomatopoeia.
The quotation given for alliteration, "the stuttering rifles' rapid rattle", followed by "the monstrous anger of the guns", is an example of more than alliteration: it is also an example of Owen trying to say what a battlefield of the First World War sounded like; in AWE's view, he is remarkably successful in distinguishing between the deep, dull boom of heavy artillery ("monstrous anger of the guns") and the crisper, sharper crackling of the ordinary soldiers' rifles. Onomatopoeia is often reinforced by alliteration.
Etymological note: The word onomatopoeia came into English through Late Latin from the ancient Greek. It is a transliteration of the Greek όνοματοποιία (onomatopoeia), which is a compound of the noun ὄνομα (onoma, ‘name’, ‘word’) and the verb ποιεῖν (poiein, ‘to do’, ‘to make’) and was used, like its English descendant, to mean ‘the coining of a word in imitation of a sound’.