means a short period of sleep, usually taken during the day rather than at night.

from From Old English hnappian, 'to doze or slumber lightly,' a word that seems to share roots with the old Germanic and possibly Dutch and German cousins for nodding off (German nicken, Dutch knappen have been suggested as relatives). The 'fabric nap' — the fuzzy raised surface on cloth — is a completely separate word, despite the spelling collision, so resist the temptation to imagine the two are related.