from The American Heritage® Dictionary of the English Language, 4th Edition
- adv. Slang Squarely; directly: stood smack-dab in the middle of the freeway.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. Exactly; directly; precisely; dead-center.
smack1 + dab1, with a sudden contact.(American Heritage® Dictionary of the English Language, Fourth Edition)