1A hypothetical man and woman; male and female representatives of the common or ordinary people.
2British A printed or written statement of the money owed for goods or services.
3British A pill or tablet of a recreational or non-medicinal drug; especially a tablet of heroin. Usually in plural.
Early 17th century; earliest use found in John Taylor (1578–1653), poet. From Jack + and + jill, reflecting conventional and proverbial association of the two names.