metrics n.

"science of versification," 1760, from Latinized form of Greek he metrikē "prosody," plural of metron "meter, a verse; that by which anything is measured; measure, length, size, limit, proportion" (from PIE root *me- (2) "to measure"). Middle English had metrik "the branch of music which deals with measure or time" (late 15c.), from Medieval Latin metricus.

in the names of sciences or disciplines (acoustics, aerobics, economics, etc.), a 16c. revival of the classical custom of using the neuter plural of adjectives with Greek -ikos "pertaining to" (see -ic) to mean "matters relevant to" and also as the titles of treatises about them. Subject matters that acquired their English names before c. 1500, however, tend to be singular in form (arithmetic, logic, magic, music, rhetoric). The grammatical number of words in -ics (mathematics is/mathematics are) is a confused question.