from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Wearing civilian clothes while on duty to avoid being identified as police or security: a plainclothes detective.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Wearing ordinary civilian clothes instead of a uniform, in order to avoid detection.
- n. Ordinary civilian clothes, rather than uniform.
Sorry, no etymologies found.