didactics (n.)

"fitted or intended for instruction; pertaining to instruction," 1650s, from French didactique, from Latinized form of Greek didaktikos "apt at teaching," from didaktos "taught," past participle of didaskein "teach," from PIE *dens- "to learn" (source also of Sanskrit dasra- "effecting miracles"). Related: Didactical; didactically.

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.