The word "lyric" was used for the "words of a popular song" about 1876 for the first time. The plural "lyrics" was used only in referring to the words of several songs. That it is used for the words of a single song as its "lyrics" became increasingly common (probably because of the association between "lyrics" and the plural form "words"), and is common in modern usage of today's society. Use of the singular form "lyric" is still grammatically acceptable.