Green’s Dictionary of Slang

narrowback n.

[? their stereotyped physique or Ulster dial. narrow, mean, miserly]

1. [late 19C] a supporter of political reform.

2. [1950s+] (US) an Irish person, esp. a second-generation immigrant.

3. [1950s+] (US) a Protestant.

4. [1950s+] (Irish) an immigrant who returns from the US to live in Ireland.