"pertaining to historical coins and coinage," 1765, from French numismatique (late 16c.), from Latin numismat-, stem of numisma "coin, currency, stamp on a coin," from Greek nomisma "current coin, piece of money; usage," literally "what has been sanctioned by custom or usage," from nomizein "have in use, adopt a custom," from nomos "custom, law, usage," from PIE root *nem- "assign, allot; take." Earlier in the same sense was nummary (1650s), from Latin nummarius, from nummus "a coin." Numelarian (c. 1500) was a word for "money-changer," from Latin nummularius. Related: Numismatical (1716).
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.
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Definitions of numismatics from WordNet
the collection and study of money (and coins in particular);