Onomatopoeia (or rarely echoism) is a type of word, or the process of creating a word, that phonetically imitates, resembles, or suggests the sound that it describes. Common onomatopoeias in English include animal noises such as oink, meow, roar, and chirp, among other sounds such as beep or hiccup.

Onomatopoeia can differ by language: it conforms to some extent to the broader linguistic system. Hence, the sound of a clock may be expressed variously across languages: as tick tock in English, tic tac in Spanish and Italian (see photo), dī dā in Mandarin, kachi kachi in Japanese, or ṭik-ṭik in Hindi, Urdu, and Bengali.

The word onomatopoeia, with rarer spelling variants like onomatopeia and onomatopœia, is an English word from the Ancient Greek compound ὀνοματοποιία, onomatopoiía, meaning 'name-making', composed of ὄνομα, ónoma, meaning "name"; and ποιέω, poiéō, meaning "making". It is pronounced /ˌɒnəmætəˈpiːə, -mɑːt-/ ^ⓘ. Words that imitate sounds can thus be said to be onomatopoeic, onomatopoetic, imitative, or echoic.

In the case of a frog croaking, the spelling may vary because different frog species around the world make different sounds: Ancient Greek brekekekex koax koax (only in Aristophanes' comic play The Frogs) probably for marsh frogs; English ribbit for species of frog found in North America; English verb croak for the common frog.

Some other very common English-language examples are hiccup, zoom, bang, beep, moo, and splash. Machines and their sounds are also often described with onomatopoeia: honk or beep-beep for the horn of an automobile, and vroom or brum for the internal combustion engine. In speaking of a mishap involving an audible arcing of electricity, the word zap is often used (and its use has been extended to describe non-auditory effects of interference).

Human sounds sometimes provide instances of onomatopoeia, as when mwah is used to represent a kiss.

For animal sounds, words like quack (duck), moo (cow), bark or woof (dog), roar (lion), meow/miaow or purr (cat), cluck (chicken) and baa (sheep) are typically used in English (both as nouns and as verbs).

Some languages flexibly integrate onomatopoeic words into their structure. This may evolve into a new word, up to the point that the process is no longer recognized as onomatopoeia. One example is the English word bleat for sheep noise: in medieval times it was pronounced approximately as blairt (but without an R-component), or blet with the vowel drawled, which more closely resembles a sheep noise than the modern pronunciation.