Onomatopoeia, sometimes called echoism, is used both in a narrow and in a broad sense.
1. In the narrow and most common use, onomatopoeia designates a word, or a
combination of words, whose sound seems to resemble closely the sound it
denotes: “hiss,” “buzz,” “rattle,” “bang.” There is no exact duplication, however, of nonverbal by verbal sounds; the perceived similarity is due as much to
the meaning, and to the sensation of articulating the words, as to their sounds.
Two lines of Alfred, Lord Tennyson’s “Come Down, O Maid” (1847) are often cited as a skillful instance of onomatopoeia:
The moan of doves in immemorial elms,
And murmuring of innumerable bees.
Source: A Glossary of Literary Terms by M.H. Abrams