Mid 18th century; earliest use found in John Smith. As noun from Scots + Gaelic. As adjective from Scots + Gaelic. With use as adjective compare earlier Scotch Gaelic, Scottish Gaelic.
Definition of Scots Gaelic in US English:
Scots Gaelic
noun
Scottish Gaelic.
adjective
Scottish Gaelic.
Origin
Mid 18th century; earliest use found in John Smith. As noun from Scots + Gaelic. As adjective from Scots + Gaelic. With use as adjective compare earlier Scotch Gaelic, Scottish Gaelic.