naïf

from The Century Dictionary.

• Ingenuous; artless; natural: the masculine form, naïve being the corresponding feminine (but used also, in English, without regard to gender: see naïve).
• Having a natural luster: applied by jewelers to precious stones.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Having a true natural luster without being cut; -- applied by jewelers to a precious stone.
• adjective Naïve.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Naive.
• noun One who is naive.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective marked by or showing unaffected simplicity and lack of guile or worldly experience
• noun a naive or inexperienced person