naiveté

1. The state or quality of being inexperienced or unsophisticated, especially in being artless, credulous, or uncritical.
2. An artless, credulous, or uncritical statement or act.

[French naïveté, from Old French naivete, native disposition, from naif, artless. See naive.]

Definition: innocence, gullibility
Antonyms: experience, leeriness, skepticism, sophistication

The noun has one meaning:

Meaning #1: lack of sophistication or worldliness
  Synonyms: naivety, naiveness
  Antonym: sophistication (meaning #4)