Green’s Dictionary of Slang

craw-thumper n.

[SE craw, the stomach + SE thumper, lit. breast-beater; Catholics were heavily represented among the founders of the colony that became the state of Maryland]

1. [late 18C+] a Roman Catholic.

2. [mid-19C+] (US, also claw-thumper) a native of Maryland.

3. [20C+] (Aus./Irish) an overtly pious individual.