1680s, "not confined to or following any one model or system," originally in reference to ancient philosophers who selected doctrines from every system; from French eclectique (1650s), from Greek eklektikos "selective," literally "picking out," from eklektos "selected," from eklegein "pick out, select," from ek "out" (see ex-) + legein "gather, choose," from PIE root *leg- (1) "to collect, gather." Broader sense of "borrowed from diverse sources" is first recorded 1847. As a noun from 1817.
-ism
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.