A.T. Robertson Commentary Acts 4:24

"And they, when they heard it, lifted up their voice to God with one accord, and said, O Lord, thou that didst make the heaven and the earth and the sea, and all that in them is:" — Acts 4:24 (ASV)

With one accord (ομοθυμαδον). A concert of voices as already seen by the word in 1:14; 2:46 and later in 5:12; 7:57; 15:25.

O Lord (Δεσποτα). Our word despot. Old word for relation of master to slaves or household servants (1 Timothy 6:1; 2 Timothy 2:21; Titus 2:9; 1 Peter 2:18). Simeon thus addressed God (Luke 2:29). So in 2 Peter 2:1; Jude 1:4; Revelation 6:10. See "slaves" in verse 29.