from The American Heritage® Dictionary of the English Language, 4th Edition
- adv. Informal With great speed.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. Quickly; as fast as possible; in short order.
from The Century Dictionary and Cyclopedia
- Headlong; very fast.
lickety, very fast, alteration of lick, fast (dialectal) + split.(American Heritage® Dictionary of the English Language, Fourth Edition)
First attested about 1860, in the US, as a fanciful alteration of lick and the verb split. lick appears to have something to do with animals made to go faster by means of a "lick" of a whip, although it may have also originated due to a preference for rapid licking (the "quick lick"). (Wiktionary)