from The American Heritage® Dictionary of the English Language, 4th Edition
- adv. During the nighttime on every day or most days: She works nights at the restaurant.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. At night.
- adv. Every night.
- n. Plural form of night.
from The Century Dictionary and Cyclopedia
- At night; by night.
night + -s. See -s (Etymology 3) (Wiktionary)
See night (Wiktionary)