plural of -ic, representing Latin-ica (< Greek-ika, neuter plural of -ikos), as in rhētórica (plural) rhetoric book
Nouns ending in -ics that name fields of study, sciences, arts, professions, or the like are usually not preceded by an article and are used with a singular verb: Acoustics (the science) deals with sound. Politics (the art of government) fascinates me. In certain uses, often when preceded by a determiner like the, his, her, or their, most of these nouns can take a plural verb: The acoustics (the sound-reflecting qualities) of the hall are splendid. Their politics (political opinions) have antagonized everyone.
in the names of sciences or disciplines (acoustics, aerobics, economics, etc.) it represents a 16c. revival of the classical custom of using the neuter plural of adjectives with -ikos (see -ic) to mean "matters relevant to" and also as the titles of treatises about them. Subject matters that acquired their names in English before c.1500, however, tend to remain in singular (e.g. arithmetic, logic).