Etymology of Rap

[Barnhart]

_The Barnhart Dictionary of Etymology_ reports the following at _rap_:

To talk or converse informally; chat.  1929 in Damon Runyon's writings;
later popularized in American English (about 1965), possibly by way of
Caribbean English, from the earlier British slang sense of say or utter
(1870), originally with the specific meaning of let off (an oath, etc.)
sharply, vigorously, or suddenly (1541), an expressive use of _rap_
knoch sharply.

David K. Barnhart, Editor
The Barnhart Dictionary Companion [quarterly]
barnhart at highlands.com
www.highlands.com/Lexik

"Necessity obliges us to neologize."
Thomas Jefferson-August 16, 1813