from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Informal Troublesome; annoying: a pesky mosquito.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Annoying, troublesome, irritating.
from the GNU version of the Collaborative International Dictionary of English
- adj. Pestering; vexatious; troublesome. Used also as an intensive.
from The Century Dictionary and Cyclopedia
- Troublesome; annoying; plaguy.
- Excessively: as, pesky slow.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. causing irritation or annoyance
Probably alteration of pest.(American Heritage® Dictionary of the English Language, Fourth Edition)
Possibly from pesty. (Wiktionary)