"one who maintains that, by the dispensation of grace, the moral law is not binding on Christians," 1640s, from Medieval Latin Antinomi, name given to a sect of this sort that arose in Germany in 1535, from Greek anti "opposite, against" (see anti-) + nomos "rule, law," from PIE root *nem- "assign, allot; take." As an adjective from 1640s.
word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.
Others are reading
Definitions of antinomianism from WordNet
the theological doctrine that by faith and God's grace a Christian is freed from all laws (including the moral standards of the culture);