c.1300, "individual, unbroken, unmarried," from Old French sengle "being one, separate," from Latin singulus "one, individual, separate" (usually in plural singuli "one by one"), from sim- (stem of simplus; see simple) + diminutive suffix.
Meaning "unaccompanied or unsupported by others" is from mid-14c. Single-handed is first attested 1709. Single-parent (adj.) is attested from 1969.
late 15c., "the middle or outer claw on the foot of a hawk or falcon," from single (adj.). Given various technical meanings from 16c. Sports sense is attested from 1851 (cricket), 1885 (baseball). Meaning "phonograph record with one song on each side" is from 1949. Meaning "unmarried person" is from 1964; singles bar attested from 1969. An earlier word for "unmarried or unattached person" is singleton (1937).
"to separate from the herd" (originally in deer-hunting, often with forth or out), 1570s, from single (adj.). Baseball sense of "to make a one-base hit" is attested from 1899 (single (n.) "one-base hit" attested from 1885). Related: Singled; singling.