Father To Son

Luke 20:42 ESV

42 For David himself says in the Book of Psalms,

 “‘The Lord said to my Lord,

Sit at my right hand,

Luke 20:43

43 until I make your enemies your footstool.’

The same Greek word is used for both Lords in this passage. It is the one God speaking to Himself, Father to Son. 

CWS:

 [ art,nn G2962 κύριος * kurios * koo'-ree-os * From κῦρος kuros (supremacy); supreme in authority, that is, (as noun) controller; ...