Concise Bible Dictionary:

The word εὐσέβεια,—βέω, signifies “to exercise piety, reverence”: a reverential sense of having to say to God, which should be shown by the creature to the Creator, and which should especially characterize the saints towards God their Father and to the Lord Jesus. The word is translated “piety” in the AV only in 1 Timothy 5:44But if any widow have children or nephews, let them learn first to show piety at home, and to requite their parents: for that is good and acceptable before God. (1 Timothy 5:4). It is rendered “holiness” in Acts 3:1212And when Peter saw it, he answered unto the people, Ye men of Israel, why marvel ye at this? or why look ye so earnestly on us, as though by our own power or holiness we had made this man to walk? (Acts 3:12) and “worship” in Acts 17:2323For as I passed by, and beheld your devotions, I found an altar with this inscription, TO THE UNKNOWN GOD. Whom therefore ye ignorantly worship, him declare I unto you. (Acts 17:23). In all other places it is “godliness.” “Piety” is a better translation, and distinguishes it from θεοσέβεια, which signifies “worship, or fear of God,” and is translated “godliness” in 1 Timothy 2:1010But (which becometh women professing godliness) with good works. (1 Timothy 2:10).