1632, probably of imitative origin, similar to Low Ger. slappe, Ger. Schlappe. The noun is recorded from 1648; fig. meaning "insult" is attested from 1736. Slapdash (1679) is first attested in Dryden. Slap-happy (1936) originally meant "punch-drunk." Slapshot in ice hockey is recorded from 1942. Slap on the wrist "very mild punishment" dates from 1914.
Precisely; directly: Streets that ended slap in a courtyard/ The storm was pointed slam-bang at Tampa(first form 1829+, second 1885+, third 1940s+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with slap down
Restrain or correct emphatically, as in They thought he was getting far too arrogant and needed to be slapped down. This idiom, which literally means “inflict a physical blow,” began to be used figuratively in the first half of the 1900s.