"Lyric" derives via Latin lyricus from the Greek λυρικός (lyrikós), the adjectival form of lyre. It first appeared in English in the mid-16th century in reference, to the Earl of Surrey's translations of Petrarch and to his own sonnets. Greek lyric poetry had been defined by the manner in which it was sung accompanied by the lyre or cithara, as opposed to the chanted formal epics or the more passionate elegies accompanied by the flute. The personal nature of many of the verses of the Nine Lyric Poets led to the present sense of "lyric poetry" but the original Greek sense—words set to music—eventually led to its use as "lyrics", first attested in Stainer and Barrett's 1876 Dictionary of Musical Terms. Stainer and Barrett used the word as a singular substantive: "Lyric, poetry or blank verse intended to be set to music and sung". By the 1930s, the present use of the plurale tantum "lyrics" had begun; it has been standard since the 1950s for many writers. The singular form "lyric" is still used to mean the complete words to a song by authorities such as Alec Wilder, Robert Gottlieb, and Stephen Sondheim. However, the singular form is also commonly used to refer to a specific line (or phrase) within a song's lyrics.