moral compass

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

• noun idiomatic, ethics An inner sense which distinguishes what is right from what is wrong, functioning as a guide (like the needle of a compass) for morally appropriate behavior.
• noun idiomatic, ethics A person, belief system, etc. serving as a guide for morally appropriate behavior.
• noun archaic, idiomatic, ethics The full range of virtues, vices, or actions which may affect others and which are available as choices (like the directions on the face of a compass) to a person, to a group, or to people in general.