n. & adj. — originally Science
an invariant method of establishing time that is used as a reference point for timekeeping around the globe.
Type: 1. Origin — Standard Time is a concept devised by Sir Sanford Fleming (1827-1915), a Canadian railway surveyor and engineer, who in 1879 proposed and began to promote standard time zones attached to the Greenwich meridian (see the quotations). The idea caught on fast. By the early 1880s, most countries had adopted the concept as a temporal reference point (see, e.g. the 2016 quotation).
COD-2 lists the term, s.v. "standard time", but does not mark it in any way.