1579, the oral rendering of the arithmetical sign
+, from L.
plus "more" (comparative of
multus "much"), altered by influence of
minus from
*pleos, from PIE
*ple- "full" (see
plenary). Placed after a whole number to indicate "and a little more," it is attested from 1902. As a conj., "and," it is Amer.Eng. colloquial, attested from 1968.
Plus fours (1921) were four inches longer in the leg than standard knickerbockers, to produce an overhang, originally a style assoc. with golfers. The plus-sign itself has been well-known since at least 1489 and is perhaps an abbreviation of L.
et (see
etc.).