If someone, especially an American, is Scotch-Irish, they are descended from both Scottish and Irish people, especially from Scottishpeople who had settled in Northern Ireland.
[mainly US]
He was from an ordinary Scotch-Irish family.
Scotch-Irish is also a noun.
The first great wave of Scotch-Irish emigration began with the failed harvest of1717.
Scotch-Irish in British English
(ˈskɒtʃˈaɪrɪʃ)
adjective
1. US
descended from both Scottish and Irish people, esp from Scottish people who had settled in Northern Ireland
He was from an ordinary Scotch-Irish family.
noun
2. the Scotch-Irish
Scotch-Irish in American English
(skɑtʃˈaɪrɪʃ)
US
adjective
of those people of N Ireland descended from Scottish settlers, esp. those who emigrated to America