mechanics n.

late 14c., of a craft or skill, "pertaining to or involving mechanical labor" (a sense now usually with mechanical), also "having to do with tools," from Latin mechanicus "of or belonging to machines or mechanics; inventive," from Greek mēkhanikos "full of resources, inventive, ingenious," literally "mechanical, pertaining to machines," from mēkhanē "device, tool" (see machine (n.)). Meaning "of the nature of or pertaining to machines" is from 1620s.

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.