notion (n.)

late 14c., nocioun, "a general concept, conception," from Latin notionem (nominative notio) "concept, conception, idea, notice," noun of action from past participle stem of noscere "come to know," from PIE root *gno- "to know." Coined by Cicero as a loan-translation of Greek ennoia "act of thinking, notion, conception," or prolepsis "previous notion, previous conception."

Meaning "an opinion, a view, a somewhat vague belief" is from c. 1600; that of "a not very rational inclination, a whim" is by 1746. Notions in the concrete sense of "miscellaneous small articles of convenience or utensils" (such as sold by Yankee peddlers) is by 1803, American English, via the idea of "clever product of invention."