noun (n)

• the quality of being enduring and free from change or variation(noun.attribute)

  Example:
  Early mariners relied on the constancy of the trade winds.
  

  Synonym:
  stability
  Antonym:
  changefulness, inconstancy
  

  source: wordnet30
• (psychology) the tendency for perceived objects to give rise to very similar perceptual experiences in spite of wide variations in the conditions of observation(noun.cognition)

  Synonym:
  perceptual constancy
  

  source: wordnet30
• faithfulness and dependability in personal attachments (especially sexual fidelity)(noun.attribute)

  source: wordnet30
• The state or quality of being constant or steadfast; freedom from change; stability; fixedness; immutability; as, the constancy of God in his nature and attributes.(noun)

  source: webster1913