Scots

late Old English Scottisc, "of Scottish nationality; found or done in Scotland;" see Scot + -ish. Related: Scottishness.

"of Scotland," 1590s, a contraction of Scottish. As a noun, by 1743 as "the people of Scotland collectively;" 1700 as "the sort of English spoken by the people of Scotland." 

Scots (mid-14c.) is the older adjective, which is from Scottis, the northern variant of Scottish. Scots was used in Scottish English until 18c., then Scotch became vernacular, but in mid-19c. there was a reaction against it because of insulting and pejorative formations made from it by the English (such as Scotch greys "lice;" Scotch attorney, a Jamaica term from 1864 for strangler vines).

Scotch-Irish is from 1744 (adj.); 1789 (n.); more properly Scots-Irish (1966). Commercial Scotch Tape (1945) was said to be so called because at first it had adhesive only on the edges (to make it easier to remove as a masking tape in car paint jobs), which was interpreted as a sign of cheapness on the part of the manufacturers. It had become a verb by 1955 and for a time was often printed without capitals.

"native of Scotland," late 14c., from Scots + man (n.). Scotswoman is by 1820.