from
The Collaborative International Dictionary of English v.0.48
Know-nothing \Know"-noth`ing\, n.
A member of a secret political organization in the United
States, the chief objects of which were the proscription of
foreigners by the repeal of the naturalization laws, and the
exclusive choice of native Americans for office.
[1913 Webster]
Note: The party originated in 1853, and existed for about
three years. The members of it were called
Know-nothings, because they replied "I don't know," to
any questions asked them in reference to the party.
[1913 Webster]