Onomatopoeia occurs when a word resembles or suggests the sound it is describing. Onomatopoetic language is used to make writing more expressive and dynamic. When identifying onomatopoeia, it is important to stick to clear and obvious examples rather than words that “could be” onomatopoeia or sound like “soft” onomatopoeia.
“How they clang, and clash, and roar!” from Edgar Allan Poe’s “The Bells”
“He sheathed his sword”
Though you could argue that “sheathed” sounds vaguely similar to the sound made when a sword is put away, it is not a strong example of onomatopoeia.