from
The Collaborative International Dictionary of English v.0.48
Rap \Rap\, n. [Perhaps contr. fr. raparee.]
A popular name for any of the tokens that passed current for
a half-penny in Ireland in the early part of the eighteenth
century; any coin of trifling value.
[1913 Webster]
Many counterfeits passed about under the name of raps.
--Swift.
[1913 Webster]
Tie it [her money] up so tight that you can't touch a
rap, save with her consent. --Mrs.
Alexander.
[1913 Webster]
{Not to care a rap}, to care nothing.
{Not worth a rap}, worth nothing.
[1913 Webster]