The English noun "belief", "faith" or "faithfulness" translates to the Greek words πίστις, εως, ἡ (transliterated as "pistis") which means:

faith, belief, trust, confidence; fidelity, faithfulness -- Strong's Concordance

The English verb "believe" translates to the Greek word πιστεύω which means:

to believe, entrust -- Strong's Concordance

Trust in the Lord with all your heart, and do not lean on your own understanding. -- Proverbs 3:5 (ESV)